I’m sorry to hear about this, @Phillip!
You mention that switching to the 2015 theme did not help—what do you find if you do similar testing with all of the other plugins on your site?
For a full and comprehensive test here, I would recommend doing all of the steps outlined here: https://theeventscalendar.com/knowledgebase/testing-for-conflicts/
After EACH STEP in that process, check on your month view and try paginating through the months again—how do things behave? Do things improve anywhere along the way with your testing?
I only suggest this testing because there is not a known bug like this at this time, and I cannot reproduce this behavior on my own testing site whether logged in or logged out.
Let us know what you find!
Thank you,
George