Problems with the disappearance of multicast in the final equipment?

Question

Computer networks

1 - Encoder
2 - Cisco switch
3 - Multiplexer

Good afternoon everyone. There was a problem of the following nature:
The encoder (1) processes the content and sends multicast traffic to the multiplexer (3) through the Cisco switch (2), from time to time in the multiplexer (3) the multicast traffic from the encoder (1) disappears or partially does not reach.
PS. I looked in the switch, multicasts are present there and are requested normally. The problem arose recently, before that it worked fine for 3 years.

Do you have any idea what could be the source of the problem?

Answer 1

from time to time in the multiplexer (3) multicast traffic from the encoder disappears or partially does not reach

How often? What did they check?
All channels or selective?
Is it possible to turn on a test computer with VLC in Cisco and monitor channels there?