DVB-C2 capability is disabled. I believe it has caused issues in the (distant) past. I tried enabling it and scanned again. Same result: 434000 does not work but 138000 does. Hence I disabled again since it seems to make no difference.
When scanning based on the 138000 NIT table I did not notice any missing channels on the 434000 frequency (didn't look for it either). In order to identify which channels that sits on the 434000 frequency, I installed an old version of DVBLink Server / TVSource. The program allow to easily see what channels sits on which frequencies. Interestingly ebough, DVBLink was able to find a NIT table on 434000. Its a two-step process. First it scans based on 434000 / 6875 / QAM64 and then the user is prompted to select the Network ID (see attached picture 1). I then went on and scanned for channels and again it was able to scan the 434000 frequency and find its channels (refer to pictures 2 and 3). Further into the setup process I was able to identify the three channels on the 434000 frequency (picture 4), and having completed the setup I was able to watch them (picture 5).
Going back to MC25 I noticed that EPG data was missing from the three channels (remember they were already setup during a channel scan completed some time ago before testing out the new NIT scan). Further, I was unable to watch them. I then checked my TV set (so normal TV - not TV via PC software), which has no problem displaying the channels nor their EPG data.
Since a normal TV as well as another software suite has no problems, to me it looks like it is MC25 that has some kind of bug. Why it shows on this particular frequency 434000 I have no clue.
Further, the other frequencies you mentioned failed tuning also failed in DVBLink.
Hope it helps...