[fredplaysguitar]

Wow!!  I had the same issue with a newer off-brand Android tablet, and could not figure out how to fix Mobile Sheets to stop automatically adding in periods when I wanted to annotate some new chords, separated by a lot of periods.  I Googled for an answer and came here to MY OWN ANSWER from years ago!!  This actually is the solution.  It's in the Android's keyboard settings of the tablet, not within MS itself.  

I can't believe I forgot my own solution!  Oh, wait...  I'm getting older so the memory is fading!!