High CPU of init process

I see periodical high CPU usage of init process from some (one or more, but not all) containers on some servers (but not all servers).

latest LXD from snap. It happens with all stable versions at least few months. What can be wrong?

top - 18:10:02 up 64 days, 15:58,  1 user,  load average: 4.62, 4.25, 4.35
Tasks: 1297 total,   4 running, 1293 sleeping,   0 stopped,   0 zombie
%Cpu(s): 16.2 us, 10.1 sy,  0.0 ni, 73.0 id,  0.7 wa,  0.0 hi,  0.0 si,  0.0 st
MiB Mem :  64213.8 total,   1103.8 free,  46952.8 used,  16157.3 buff/cache
MiB Swap:  32106.9 total,  30609.4 free,   1497.5 used.   3859.9 avail Mem

    PID USER      PR  NI    VIRT    RES    SHR S  %CPU  %MEM     TIME+ COMMAND
 636794 1000000   20   0   33256   2036    984 R  99.7   0.0  23450:14 init
...