Hi Lisa,
If the error messages are random, then it is most likely a server related issue – likely a shared hosting throttling (if your are on a shared host), or low memory or something in relation to those. If it was a plugin related problem, it would be possible to replicate it 100 out of 100 times. There is unfortunately nothing I can do to prevent issues with the underlying architecture.
The good news is, that we are preparing a new release, where this error message no longer appears. Instead, the search will gracefully stop. It will not fix the underlying issue, but at least the warning message goes away, making the temporary problem unnoticable for users.