Tvheadend

Hi

I've spend most of the weekend setting up my Wetek Play box with built in dual DVB-S tuners running OpenElec 6.0.3.
On the outside I have a 90cm dish with Duo LNB Quad (2 LNB's, 4 COAX outs), the LNB has been installed according to the installation instructions (see this link (http://www.canaldigitaal.nl/uploadedfiles/content/others/installatiehandleiding-duo-lnb.pdf), sorry but could only find Duch instructions), which say to mount the LNB with the 23.5 head in the mounting clamp, and then turning the LNB until the line on it is level.

At this point only 1 of the 2 DVB-S tuners in my wetek box is connected to the LNB

I setup TvHeadEnd and OSCam as documented in various guides available.
I added 2 networks, one for 19.2 and the other for 23.5

All seems to be working, meaning I can watch streams from both 19.2 and 23.5 networks.
I didn't check all streams, but the ones I did check have clear picture with nu freezes or anything.
When watching a stream and checking the status page in TvHeadEnd, SNR is about 85-90% and signal strength about 75%

however I seem to be having 2 problems:
1. Some muxes are failing to scan, both on 19.2 and 23.5 networks. Currently I have 17 failed muxes on 19.2 and 35 failed on 23.5. When trying to do a rescan of these muxes (by setting scan status to 'PEND' when editing the mux) I get the same result in the log for every mux:

2016-07-17 21:43:06.000 mpegts: 11836H in Astra 23.5 - tuning on Availink AVL6211+AV2011 DVB-S/S2 : DVB-S #0
2016-07-17 21:43:06.023 subscription: 0034: "scan" subscribing to mux "11836H", weight: 5, adapter: "Availink AVL6211+AV2011 DVB-S/S2 : DVB-S #0", network: "Astra 23.5", service: "Raw PID Subscription" 
2016-07-17 21:43:16.000 mpegts: 11836H in Astra 23.5 - scan no data, failed
2016-07-17 21:43:16.000 subscription: 0034: "scan" unsubscribing

I tried searching the the 'scan not data, failed' logging, but came mostly across TvHeadend bug reports and forum posts from people getting nothing at all working, which is not the case for me.
Could this error be caused by an incorrectly positioned dish or LNB? Or is something else wrong?

2. I am missing some channels/services I would expect to receive:
One specific example: Belgium TV channel 'Een' (http://www.onastra.com/16665077/channels?free=no&pay=yes&mode=tv&package=84&sd=yes&hd=yes#!/channel/16977)
Its frequency (12188H) was not in my muxes list (I chose to add predefined muxes when configuring my networks).
Is this normal? I tried adding the muxes manually, but then they fail with same error as described in my first problem.
What other (besides several other channels I'm missing) channels could I be missing, which seem not to be in the predefined muxes list?

Thanks a lot for any helping comments, I'm really at my wits end after a whole day of searching...