Vector_

I assume you mean 91.70.
You could install the bug-fixed version of 391.70, called 491.70 above. Or you could use either of patched firmwares versions  273.63 or 373.63; use 373.63 (fixed 200V minimum MPPT voltage) unless you have panels with often less than 200 V, in which case try 273.63. Or you could use factory firmware version 73.63, and put up with the stuck at 90 V problem.
Edit: Actually @Vector_, what is your lowest typical MPPT voltage? 200 V may be too high, and if 291.70 doesn't work for you, then 273.63 is unlikely to work either. I could make a lower voltage version of 373.63 if needed.

The good news: you can update to patched firmware version 373.63.
The bad news: There is factory firmware version 73.06 available that is slightly (1 month) later than 73.63. So I might get around to patching that one day.
Also bad: 373.63 doesn't have the complete set of patches; 291.70 has slightly more patches. I have no idea how significant those extra patches are, sorry.
Also good to know: If you have a small number of panels, like 4S or 5S such that you don't reliably get to 200 V with some level of clouding, you could also update to patched firmware version 273.63, which does not have the minimum MPPT voltage change, only the current threshold change.