I found an instance where the "workaround" also fails. BarCounter absolutely does not like to precede the MMR plugin in a measure. To correct the problem, I added an instance of BarCounter after each measure containing MMR (which worked). Experimenting, I moved the "workaround" back one measure (to avoid the MMR). Problem also went away. I adjusted the previous-posted failing score for illustration.
Hello there, HM. I've stripped down the score to just one failing instrument (the tuba, of course). It's pretty straightforward. Hopefully, it will reliably fail for you, too.
I have encountered a small bug. I insert a "Boundary Change" to drop the start of the staff on the page. This is followed a couple measures in with a "Boundary Change Reset" to return to the staff default. The BarCounter is inserted as you would think, at the beginning. Occasionally, a measure number is skipped over, eg, the measure count goes form 7 to 9. It doesn't seem to be predictable. When I scroll slowly to find where the problem lies, everything looks normal until one final scroll arrow click causes all the measure numbers to vanish momentarily and then reset to the +1 values.
As a workaround, I found that if I immediately follow the "Boundary Change reset" with an additional instance of BarCounter, everything works perfectly. [Version 0.3}