Thank you for showing interest in our plugin.
The error generated should not be affecting the plugin operations and all should work fine, though I do not know why such error is popping up. At this stage there are 2 options to find what is causing it:
1. Or wait for the next version of the plugin which is to be released this week or next week and confirm if the issue persists.
2. Alternatively you can contact us on email@example.com and we can explain to you how to enable WordPress debug logging and once you reproduce the issue, we will look into the logs maybe we will identify the issue.
Hope the above helps...