Does it happen if using eSpeak or Windows OneCore? And with those, if it does still happen, if you after that press NVDA+q then down arrow to "restart with add-ons disabled and debug logging" does it STILL happen?
That will help narrow down whether it is AN add-on, the Eloquence add-on (and to be clear, is this the legal Code Factory SAPI 5 or the less legal one we don't talk about?), or something else.
If you CAN reproduce it with add-ons disabled, then could you send us a copy of the generated debug log to
in...@nvaccess.org (you will find the log in your %temp% folder - note the percent signs).
Kind regards
Quentin