Load test with subscribe/unsubscribe/publish

I have to following problem: During an implementation of "lock" function, I am using subscribe/unsubscribe/publish method, not to pull continuously the state of the lock.
What I experience, that I register a handler with SubscribeAsync, multiply times (4) times, so I get an event, when the lock is unlocked. All parallel locks trying to get the lock, should get this event due to the registration. Using redis monitor, I can see that the "SUBSCRIBE" command is received.
But at the time of publish, usually, only 2 handler is only getting the event, and not 4 of them. (sometimes I got all 4 of them, sometimes 3 of them)
What I also tried, was to issue the SubscribeAsync double (exactly after each other), in this case the interesting is that I got 6 events, 2 doubles, and 2 singles. This means for me that all 8 subscribe should have been called, as not a pair (double calling) dropped out, but a part of it.
I assume, that the StackExchange.Redis collects all my subscribe handlers, and if event is coming from the redis, then not redis is responsible for calling each handler, but redis only calls the StackExchange.Redis handler, which calls my all handlers.
Is there a way to check if my handlers has been registered? And if not why? How can I stabilize it?
I am using windows 11, with Visual studio 2022, .Net8, using a local windows redis server SE.Redis-v2.7.33.41805
I am welcoming any suggestions

Start by reproducing the report with four parallel SubscribeAsync registrations and a publish operation while watching the local Redis server with Redis MONITOR. Compare the number of Redis subscriptions and delivered callbacks, then determine whether the loss occurs in Redis or the StackExchange.Redis client. Done means the cause is identified and the issue has a verified fix or reproduction-based explanation.