based on very limited experience:
I've been using the green lid sheetrock-brand premixed joint compound when I tape, and have had no bubbles.
However, I forgot to tape (ahem) on one joint & decided to add tape and used the blue-lid sheetrock-brand premixed joint compound. I got several bubbles. Luckily, I spotted most, pulled up the tape, added more joint compound, and fixed the problem (well, one remains that I'll have to fix).
I'm wondering whether the different joint compound caused the problem? Any thoughts based on more experience than me?