At technocrat mentions, a good way to get help to sort this is to offer a reprex of the problem and then folks can try to disagnose the issue.
Right now, there's not much to go on other than to google for related keywords.
Regarding the potential that it's a bug, that's certainly a possibility, but I don't see any promising leads of existing reports https://github.com/rstudio/shiny/issues?utf8=✓&q=is%3Aissue+++includeMarkdown
I'm sure the shiny folks would welcome a bug report, but they'd likely need a reprex too to reproduce and diagnose the issue.
Anyway you can create a mininal reprex in something like rstudio.cloud, and then share the public project?