incoming caller ID with Response Group showing number from previous call (PSTN only!)

Dear Community,

we are facing a issue since about 11/2021 that incoming calls through RGS showing the false number. users only get the last telephone number from the previous call with new calls.

all log files (like reporting database, or local s4b logs) are showing correct telephone numbers to the calls. only the S4B Client itself shows the previous caller id on an active call.

the "standard" troubleshooting steps are already done (like clearing cache, etc...) - but this does not help.

the problem seems similar to following threads:

https://docs.microsoft.com/en-us/answers/questions/278753/incoming-caller-id-with-response-group-showing-sam.html

https://docs.microsoft.com/en-us/answers/questions/520062/caller-id-issue-when-a-call-is-received-to-a-respo.html

does anybody have similar issues...? or better, are there some solutions?

overview:

S4B 2019 Standard with May 2021 Update

Office 365 semi-annual channel (so version 2021)

s4b client: 16.0.13801.21148

We will try to update to the latest S4B Server Update (12/2021) because there are many fixes... but there is nothing in the change log which indicates a fix for this issue.

Thanks!