Having another look at your previous post, with GetAllSubscriptionInfos, using MONITOR will show the related Redis commands to what your application is doing. You can then relate those commands to the Redis documentation with Time Complexity which should help you identify which commands are causing your high CPU usage on Redis.
I can only guess what it might be but since GetAllSubscruptionInfos calls ScanAllKeys, I’m pretty sure that will be your problem if you are still running that on every OnUnsubscribeAsync event.
Scanning all channels and returning all results every time someone connects or reconnects could lead to high load causing further problems. For example, it could result in client timeouts which might result in clients trying to reconnect leading to more load putting your system into a loop it can’t break without shedding lots of users.
Running UnRegisterExpiredSubscriptions when someone logs could also lead to additional scans.
These are all guesses that you will need to check with observations using logging and tools like MONITOR command for Redis. Once you’ve found the root cause, you’ll have a baseline to work with to iterate and test alternate solutions as you go. The more you can measure/observe, the easier that will be.