Recent android phone.
I initially observed this issue just with Boom and Megaboom bluetooth speakers, but I now have Jabra buds, and see the same issue:
The first 100-500 milliseconds of audio do not play.
This is an issue if it is a language app (that says a word), or a workout app (that says "start" and then 30 seconds later says "stop") because all or most of the sound does not play at all.
What is the resolution?
I have been forced to use wired buds for language learning (which is NO fun!)
When I used apple airpods I did NOT have this issue. (I no longer use airpods because they cannot be repaired or battery-replaced)