As @matt1 already said please don’t just post here but open a new thread.
Read How to ask a good question / Help Us Help You - Tutorials & Examples - openHAB Community before you do.
I suggest you move to openHABian as the basis of your box first.
It’s a known setup then that people here can help you with while only you know all the details you have configured on your current system. A RPi3 can handle OH but it’s a little ‘edgy’ so you have to be careful with all the config details to affect memory use.
These are of importance when looking after issues with performance like you do but noone wants to start a lengthy Q&A for this.
PS: Just flash latest openHABian image to a new SD (a 16GB will do BTW, or get an ‘endurance’ tagged SD model) and export + import your current config.
When you do, also re-do your SD setup. System on USB is as unreliable as on internal.
Check out openHABian | openHAB and go for SD mirroring.