I noticed my Arduino (esp3288) devices going offline “for no reason” avery few days.
This correlates with my 3D-Printer being used.
And I think sometimes it is because my fridge is starting to cool.
So yes, this can happen.
But I am no expert.
That is why, personally I have avoided Wi-Fi and have not yet tried Zigbee devices.I think Zigbee should have less interference due to the narrow bandwidth used.
Most all my Smart Home things to date are Z-Wave.
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I bet there is a suppression that could be added. I wonder as an easy experiment could you try adding a ground wire to the washer frame? If the frame is metal it may act like a faraday cage and keep the signal attenuated.
Electrical filtering AND faraday cage may be needed.
Depending on the layout of your house, this might be solvable with a mesh router. My home is square, and the kitchen is right in the middle of it. So I’m using mesh not to extend my WiFi range, but to go around the obstacles presented by my refrigerator, stove, dishwasher, and microwave.
Not if the motor is spraying random interference all across the spectrum.
At work, we suddenly had complaints about a 2.4 GHz AP. We found out somebody had placed a microwave oven under the AP. There was definitely enough Wi-Fi strength but there was no communication. We moved the AP elsewhere to resolve the issue.
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Classic.
We knew it was a lunch room, but it did not initially have any microwave oven.
Sometimes life is stranger than fiction. We had another case where a staff member had his own AP connected to the network through his phone. We had the HelpDesk call them & they tried to deny it. We then told them we knew it was connected to the phone. Their boss was not happy about that one!
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For best possible WiFi:
Keep the radio transmitter count low, use good radios and feed them over PoE.
A mesh will always increase interference and noise.
That’s wrong. Proper meshing means to direct clients to the closest AP, allowing to reduce transmission power and distance hence reducing overall interferences.
Of course you must not interconnect your APs via WiFi but use cables there.
PS: don’t forget to wear your alloy hat mask
PPS: SCNR
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They can only TRY to direct though. In Wi-Fi the client makes any roaming decision. Enterprise systems have proprietary “tricks”: to convince the client to roam.
No, I am quite shure on this 
More radios and more signal hops gives the result.
Then why, in our football stadium, do we have a bunch of APs placed under the seats? Low transmitter count is not a factor unless you are referring to 2.4 GHz only. There are only 3 non-interfering channels in the US. One of my neighbors with a misconfigured router interferes on 2 of them 
It may be best to leave RF discussions to wireless engineers.
I am one of those
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I work with Wi-Finas well as being an FCC licensed Broadcast Engineer. Perhaps Wi-Fi behaves differently than some other RF sources.
In another life, I was a mainframe field service engineer. You know, like in the old movies, room full of whirring tape decks and ominous boxes with twinkly lights, punchcards, 24 hour workload.
One of our babies, maybe once every couple of weeks, crashed at breakfast time. Never the same crash, analysis of many dumps just showed some random corrupt instruction in progress.
A lot of effort went into elimination and trying to identify source even before the pattern became evident. Any time between 0730 and 0830, but any random day.
Focus shifted to external causes - monitoring for mains power glitches, despite an isolated supply via motor/alternator set. The site did have serious machinery like gantry cranes, after all. Nothing.
After a year we got the companies chief designers involved, who were of course very reluctant. Not only “Stupid field engineers have missed something” but “We don’t even make that model anymore”. Corporate Sales team - who wanted to sell a million-pound replacement in future! - were able to insist.
Designers were as clueless as us field monkeys of course, but able to call on better resources. After repeating most of what we’d already done, someone borrowed a serious RF wideband monitor thingy. If I recall, a sort of didn’t really exist military secret thingy.
After a couple of days sat in the corner, this monitor caught a wideband radio scream - a nasty multifrequency blaargh - at breakfast time. Just a few hundred milliseconds. That day the mainframe did not crash, but this was at last a clue!
No-one could offer any real protection technique. The computer room was already supposedly RF screened to an extent, our supply was isolated, all the equipment cabinets properly earthed, etc. We’d been through all this already.
The design team wanted the whole building rebuilt as a huge Faraday cage.
The customer however insisted on finding the source - this was after all a government tech establishment during the cold war. It escalated to mysterious well-suited visitors who would not sign the visitor’s book because they were never really there. Whatever resources it was they deployed, the culprit was found. No Soviet spies.
About a mile away was an airfield, which did not operate at night. Each morning the tower staff switched on their ground radar. Maybe before or after coffee. The radar set had a fault. It was not supposed to connect to the dish antenna as it started up … because that would squirt out a powerful pulse sweeping across most of the RF spectrum, as some oscillator started up. Most days, the rotary dish would not be pointing in our direction when that happened…
It must have made a “click” on everyone’s radio and TV for miles around, but who would notice. Apparently the radar tech replaced some delay module costing pennies.
Which is a long story to say - @arden has done the hard part, identifying the source.
It is possible there is actually a fault in the washer - it is really not uncommon for the suppressor factory-fitted at the power inlet to burn out. It doesn’t affect operation, just leaves a smell. I have actually seen two washing machines like that.
Another maintenance issue could be worn out brushes on the motor, causing arc-sparky.
It is worth having a close look.
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That brought to mind an experience I had as a TV Broadcast Chief Engineer for a local TV station. Stations like to used licensed narrow=band microwave as a TSL (Transmitter-Studio Link) to transmit meter readings from the transmitter back to the studio. the previous engineer had not been able to get our system working reliably so we were paying for a data phone line from the transmitter.
The licensed channels are next to each other with little to no guard bands. I worked with a local RF calibration engineer to insure our equipment was running totally within its assigned band. I then contacted the manufacturer of the equipment we were “interfering” with. That station was supposed to install a filter in their receiver to narrow the reception. They were receiving too wide, into our band. Their technician said it would make no difference, but installed it anyway. We were finally able to use our equipment & cancel the phone line payment!
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I’m more curious with mainframe you worked on
I’m an engineer for big blue
Guess, from my nationality 
, period, and gov contract 
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