I'd try two things:

1. increase the debug level to 2 (or SetEnv KOHA_DEBUG 2 in the
VirtualHost if that still works) to get a full backtrace and see what
call results in a try to call clone on an undefined value;

2. check the databases for the record after each change and see
what is happening with the edited and deleted records.

Beyond that, a bit more description of how to reproduce the bug
may be needed: for example, is it NoZebra?

 Which MARC type?

If it's zebra, how is the zebra being updated? (cronjob?)