Thank you for this information!
I unfortunately still cannot reproduce the problem, and nothing in your system information looks outright problematic, so I would recommend running through the complete set of troubleshooting steps here → https://theeventscalendar.com/knowledgebase/testing-for-conflicts/
After EACH STEP in that process, open your theme customizer and see if this issue persists.
I’m sorry that this is the only available step from here, but as of now this issue is not something we can recreate and so it appears to be a code conflict. The steps I recommended above will reveal if that’s the case.
Let us know what you find!
Thank you,
George