I looked through the plugin code, and can’t find anything having to do with the error message given. Can you give me a hint as to how to track down the offending code?

This problem wasn’t happening before, and the plugin was last Updated 2 years ago, so that’s why it seems it would have to be due to PHP 7 or the most recent WordPress update. (I have not updated to 5 yet, we are using the latest 4 version.)

I realize 2 years is very old for a plugin, but it fits our needs, and I’d like to fix it, if possible. Then I could let the authors know what the problem is (they are still around, but say the problem is not caused by their plugin).

Thank you!