I have no guess what could be the reason for this behavior.
I had other issues with DigiSparks, but nothing like this.
One of my Digisparks obviously hadn't set the "self programming" fuse. The result was, micronucleus says, the download was successful, but the code didn't arrive in the chip.
This vanished after I set the corresponding fuse with avrdude.
This the best resemblance to the isssue you encounter, but not exactly.
So, no clue from me, sorry.
Harry