Preprocessing manager high CPU

[rb1980]

I've been running a zabbix server for MANY years and it has been very stable. Recently it has become extremely unstable and I have not made any changes to the configs.
When zabbix starts up, the "preprocessing manager" pegs the CPU at 100% and eventually crashes which most of the time restarts the parent process, but sometimes hangs.
This is an old, unsupported version but like said: has been very stable for many years.
Any tips on how I can tune this thing?

[rb1980]

This showed in the log on one of the crashes:

16576:20220617:120457.921 cannot read preprocessing service request
16577:20220617:120457.921 cannot read preprocessing service request
16575:20220617:120457.924 cannot read preprocessing service request
15951:20220617:120457.926 One child process died (PID:16574,exitcode/signal:9). Exiting ...
6192:20220617:120457.927 cannot write to IPC socket: Broken pipe
16192:20220617:120457.927 cannot send data to preprocessing service