[Koha] circulation.pl is maxing out the CPU - Need help!

[Chris Brown]

Gentle Reader,

We are running Koha 19.11 on Debian 9.11 (stretch). This supports 5 koha
instances for some of the volunteer-run libraries in Sheffield. It has been
stable and working fine for many months.

Recently we have seen a few instances of the server load abruptly shooting
up, maxing out the CPU and making the system unusable. Running "top" when
this happens shows that there are two instances of
/usr/share/koha/intranet/cgi-bin/circ/circulation.pl which between them are
using 100% of the CPU.

Rebooting clears the problem of course, but is not a practical long-term
solution. I am looking for suggestions as to what might be causing this or
how we might investigate further. Any help would be appreciated as this is
having significant operational impact now.

Thanks and Best Regards,

Chris Brown