Are you using the Gutenberg block editor? That editor can cause an irregular problem with auto-Tweeting, but I haven’t been able to isolate it. I can usually replicate it once or twice, then it will suddenly start working again, which doesn’t give me enough of a window to identify why it didn’t work.
Do you mean that you’re using the classic editor plug-in? If so, that shouldn’t be a problem; the changes in Gutenberg don’t effect WP to Twitter if you’re using the classic editor plug-in.