Digging into the zookeeper code, it looks like session ids consist of 8 bits of myid, time shifted 16 bits left.
The problem is that time is now 41 bits... and they shift those bits left 24, then right 8. The shift right is an arithmetic shift, so sign extension is possible. The myid bits are or'd into the upper most bits, so if sign extension happens, they will all be set to 1's. The current time, in hex, looks like this:
It would be very strange to have a time value where the upper bit of the second hex digit would be set. That will be 0x18000000000 (April, 2022), or 0xffffffffff (November, 2004)
Or, we could be using a myid up in the range of 0x80. If someone was to put the zookeeper port number (2181, or 0x885) into the myid file, that might cause this problem.