Hi, same problem.
SoftwareCenter and eopkg update-repo and upgrade says my system is up to date.
Several restarts. Broke in the middle of a coversation.
Solved the problem by setting the opusthreshold on my server to 0.
That is a bit harsh but well - it disables the old celt codec indirectly.
Something seems to be wrong with the CELT-Codec that is installed.
Perhaps wrong versions... i did not follow this to its roots.
The CELT-Codec is outdated for mumble and replaced by the Opus-Codec.
Anyway mumble is able to fall back to this codec if it is necessary to make a client
compatible with the rest of the server users. Therefor my solution will probably
relocate the problem to another user. What is not exactly nice.