There is something wrong with the latest version of dm900 drivers regarding unicable II (issue starts with October's update, but I am not quite sure about exact time). I found out that after specific time my 4 Inverto LNBs lock to single frequency (not to user band, what's strange that all 4 LNBs lock at the same frequency on which active tuner has been tuned) and I cannot tune any channel with another frequency since then. I always get "tuning failed" message. In rare cases even power off of the LNBs doesn't help (usually does). And now a little explanation why I wrote this.
A few days ago I was able to tweak the settings of PC tuning application for my PC dvb card and since then this PC card always works. It is always able to tune any frequency from any LNB even when my "LNB 4-block" is in locked state. Moreover, it unlocks it and since then it's possible to tune channels on dm900 again. It means that once the LNBs stuck on single frequency then I am able to unlock them by starting of PC tuning application. I'm almost sure that there is something wrong with the tuning in the enigma2/driver. I can see difference in PIN possibilities (PC card has specific PIN for specific user band, once I deactivate PIN then I am not able to tune it too) and yesterday I also tested the outgoing signal on my dm900 on digital scope. There is quite wide tolerance for power pulse for diseqc command. I saw that standard timing of sequence 18V-diseqc-14V should be approx. 100ms but from time to time there is almost 3-times longer time period (280ms) and regularly varies between these two values. It can be simply replicated and measured this way. I guess that there must be some side branch (or waiting loop for a driver?) which causes such difference in timing. I don't see any difference in PC tuning application, there is still the same switching interval 150ms, neither shorter nor longer. I guess that 120ms should be enough but in my case the PIN functionality is crucial otherwise I am not able to switch the channel once the LNBs lock. I use the latest experimental version from 2018/11/27, FBC S2 tuner (not S2X version) and 4x Inverto IDLU-32UL40-UNBOO-OPP LNBs. If you want, I can test it.
I tested also Unicable Editor plugin but it didn't find unicable.xml file anywhere in my /etc/ folder and it's subfolders. Maybe it works for matrix setup or switch only but my configuration is 4x LNB with combiners, splitters and power inserters.