Nextcloud OFFICE & Collabora: Exception thrown: OCP\\Lock\\LockedException

I have Nextcloud 28.0.1

I set Nextcloud Office with a separate Collabora server. Generally everything is working fine. But from time to time I can’t load the file I’m working on.

On collabora’s side I get these logs:

wsd-***** 2023-12-28 09:11:06.325386 +0100 [ websrv_poll ] INF Find or create DocBroker for docKey [https%3A%2F%2Fdomain%3A443%2Findex.php%2Fapps%2Frichdocuments%2Fwopi%2Ffiles%2xxx for session [1523] on url [https://domain/index.php/apps/richdocuments/wopi/files/xxx?access_token=xxxx&access_token_ttl=0&permission=edit]| wsd/COOLWSD.cpp:3595
wsd-***** 2023-12-28 09:11:06.325415 +0100 [ websrv_poll ] DBG Found DocumentBroker with docKey [https%3A%2F%2Fdomain%3A443%2Findex.php%2Fapps%2Frichdocuments%2Fwopi%2Ffiles%2xxx]| wsd/COOLWSD.cpp:3623
wsd-***** 2023-12-28 09:11:06.325427 +0100 [ websrv_poll ] WRN DocBroker [https%3A%2F%2Fdomain%3A443%2Findex.php%2Fapps%2Frichdocuments%2Fwopi%2Ffiles%2Fxxx] is unloading. Rejecting client request to load session [1523]| wsd/COOLWSD.cpp:3631
wsd-***** 2023-12-28 09:11:06.325489 +0100 [ websrv_poll ] ERR #19: Error while handling Client WS Request: Failed to create DocBroker with docKey [https%3A%2F%2Fdomain%3A443%2Findex.php%2Fapps%2Frichdocuments%2Fwopi%2Ffiles%2Fxxxx.| wsd/COOLWSD.cpp:5360
wsd-***** 2023-12-28 09:11:06.325508 +0100 [ websrv_poll ] ERR #19: Socket write returned -1 (EPIPE: Broken pipe)| net/Socket.hpp:1447
wsd-***** 2023-12-28 09:11:06.325527 +0100 [ websrv_poll ] ERR #19: Socket write returned -1 (EPIPE: Broken pipe)| net/Socket.hpp:1447
wsd-***** 2023-12-28 09:11:06.325540 +0100 [ websrv_poll ] WRN #19: Shutting down but 64 bytes couldn’t be flushed and still remain in the output buffer| net/WebSocketHandler.hpp:876
wsd-***** 2023-12-28 09:11:06.325556 +0100 [ websrv_poll ] ERR #19: Attempted to remove: 842 which is > size: 0 clamped to 0| net/Socket.hpp:1243
wsd-***** 2023-12-28 09:11:06.325577 +0100 [ websrv_poll ] ERR #19: Socket write returned -1 (EPIPE: Broken pipe)| net/Socket.hpp:1447
wsd-***** 2023-12-28 09:11:06.325592 +0100 [ websrv_poll ] DBG #19: Disconnected while writing (EPIPE): Broken pipe)| net/Socket.hpp:1403

the problem is solved when I restart collabora service,
what’s the problem, any help to solve this completely?

I think it’s better to ask in Collabora forum for troubleshooting advice as the issue only occurs from time to time.