Some of us started experiencing issues when iOS 13 came out. I finally figured out what the issue is and confirmed it with LingQ’s iOS developer.
It is a text-to-speech memory leak in iOS 13 that is causing this issue.
There is nothing the developer of LingQ can do about this memory leak as it’s a system issue, not an app issue.
However, if you turn the automatic text-to-speech option off in reader settings, it will stop crashing