To let you know what we have done with Cambium Support.
The problem are very high interferences. We tried different channels and downgraded to 3.5.6. Now it is working smoothly with MCS limited to 10.
This is just my personal opinion: I got a feeling that 4.4.3 is much more affected by interferences than 3.5.6 - have not yet confirmed that.
Why was there SNR 30dBm and link still not working? I think because the interfences are very high just on one site (AP's side) and SM can see AP very well, but AP can't receive SM's packets with good SNR - but we don't have that information anywhere in GUI. We have to run spectrum analyzer to assume that.
Kind regards