Trace-Log shows, that the error occurs in the jetty-api:
org.eclipse.jetty.websocket.api.UpgradeException: Failed to upgrade to websocket: Unexpected HTTP Response Status Code: 404 Site Not Found
I don’t know, if there were any changes in handling websockets…
I see that, in the jetty-upgrade-request code was a change before 8 days…perhaps this is the cause…but i am not shure. see Documented WebSocketClient. · eclipse/jetty.project@8b10f3e · GitHub
M4 lost lampbulb images from location badges. Counter (if more than 1 lamp turned on) shows but without icon. This is something with my instance or known bug?
Group:Switch:OR(ON, OFF) gGfTolietLight "Освітлення гостьового туалету" <lightbulb> (GF_Toilet, gLight) ["Lightbulb"]
Switch GF_Toilet_Light "Головне освітлення гостьвого туалету" <lightbulb> (gGfTolietLight) ["Light"]
Switch GF_Toilet_MirrorLight "Освітлення дзеркала гостьвого туалету" <lightbulb> (gGfTolietLight) ["Light"]
I’ve same error with the Innogy-Binding.
2021-05-05 17:21:01.905 [WARN ] [internal.handler.InnogyBridgeHandler] - Error starting websocket.
java.util.concurrent.ExecutionException: org.eclipse.jetty.websocket.api.UpgradeException: Failed to upgrade to websocket: Unexpected HTTP Response Status Code: 404 Site Not Found
at java.util.concurrent.CompletableFuture.reportGet(CompletableFuture.java:395) ~[?:?]
I have open an bug issue on github. perhaps somebody has a magic moment 
My system has .rules file, and (new) in M4 I get "There is no context to infer the closure’s argument types from" messages (see below) on start up. There are 40 rules in the .rules file, but only 15 such messages, so since the log entry provides no context (e.g. line number or the rule label) there is no clue which 15 of the 40 rules have the problem…
2021-05-05 15:13:11.181 [INFO ] [el.core.internal.ModelRepositoryImpl] - Validation issues found in configuration model '24g.rules', using it anyway:
There is no context to infer the closure's argument types from. Consider typing the arguments or put the closures into a typed context.
... repeated 15 times
Usually associated with as used in e.g. createTimer or forEach
The validator could be a lot more helpful though, it’s worth a github issue although no-one may be interested in DSL any more.
I knew you say that Bruce 
I do not know if DEBUG logging would give more useful information.
Ok. Thanks for the info. The rules are actually running Ok so this means there is “just” a new error (regression) in the validator code!!
Not necessarily, it might be pickier now about things that it let slide before.
Example
someGroup.members.forEach[ x | { ... process x ... } ]
At validation time, it is not possible to guess what kind of Item x will be - a Switch type perhaps, or a DateTime, or?
That means the validator can’t properly validate the processing code, is it doing legitimate things with/to x?
At runtime each member, each x, will of course be whatever it be, and you’ll either process it appropriately or blow up with an error.
To satisfy the validator, you might do something like
someGroup.members.forEach[ GenericItem x | { ... process x ... } ]
By describing the type, even as a vague default type, the validator can now work on the process.
Synology/Docker update from openhab-3.1.0.M3-debian to openhab-3.1.0.M4-debian.
Opening Basic-UI…
Error in Basic-UI
SSE-Abonnement fehlgeschlagen: Im Fallback-Modus ausgeführt
OH-log errors:
2021-05-07 11:51:30.263 [WARN ] [apache.cxf.jaxrs.utils.ResourceUtils] - No resource methods have been found for resource class org.apache.cxf.jaxrs.impl.ResponseImpl
2021-05-07 11:51:30.264 [ERROR] [org.apache.cxf.jaxrs.JAXRSInvoker ] - No subresource locator found for path /
UI on Port 8080 is not loading;
No charts within basic UI
openHAB Android-app can not connect: HTTP-Code 405
rules are running… items are refreshing…
Switching back to M3 - no errors; tried to update three times, always the same, restarting OH does not make a difference?!
What can I do???
the same here after upgrade from 3.0 to 3.1 M4
direct after start i can access the web ui, after short time nothing works anymore
17:29:30.506 [WARN ] [.apache.cxf.jaxrs.utils.ResourceUtils] - No resource methods have been found for resource class org.apache.cxf.jaxrs.impl.ResponseImpl
17:29:30.511 [ERROR] [org.apache.cxf.jaxrs.JAXRSInvoker ] - No subresource locator found for path /
browser says dev console says
GET http://192.168.179.2:8080/rest/ 405 (Method Not Allowed)
android app says
HTTP-Code 405
Hooray… I am not alone…
openHAB updated from 3.1.0.M4 to 3.1.0-SNAPSHOT (9 hours old)
→ same error 
yep i can confirm that even with AdoptOpenJDK 11, its everytime the same
i think i found the problem
do u use the hue emulation addon?
uninstall it
if you cant
service openhab stop
check if its present in /etc/openhab/services/addons.cfg and comment with # out
nano /var/lib/openhab/config/org/openhab/addons.config
delete the line with hueemulation
service openhab start
At the moment i´m on M3 again… will give it a try tomorrow, thank you
its a problem by the hue emulation
if i uninstall it and reinstall via jar file i get this
https://pastebin.com/MqC99Rjd
followed by the same error which kills rest api and basic ui
01:05:41.658 [WARN ] [.apache.cxf.jaxrs.utils.ResourceUtils] - No resource methods have been found for resource class org.apache.cxf.jaxrs.impl.ResponseImpl
01:05:41.659 [ERROR] [org.apache.cxf.jaxrs.JAXRSInvoker ] - No subresource locator found for path /
please can a dev fix this?
without hue emulation openhab is useless for my home