Further investigations on this:
1. I found TBS 6983 V20 without metal cover/shield for tuner. It got no problems with FEC 1/2 and 2/3 in CrazyScan/EBS Pro (despite lack of metal cover, in EBS Pro in BLScan2 mode)
2. I found TBS 6903 V12 with metal cover/shield for tuner. It still got problems with FEC 1/2 and 2/3 in CrazyScan/EBS Pro (only in BLScan2 mode)
So looks like not related to tuner shield. At this point, because 6983 even without metal shield got no problems and in 6903 there are no problems with TBS BlindScan I believe that this is bug in BLScan2 mode in StreamReader from crazycat (maybe related to some changes in TBS driver between 6983 and 6903, about which crazycat got no informations from TBS).
In my opinion there are two different and unrelated problems:
1. FEC 1/2 and 2/3 (DVB-S) in BLScan2 mode at StreamReader from crazycat.
2. In BLScan mode in StreamReader in 6903 for some reason step for blindscan is tied with search range (it was not for example for Prof8000), thus 1 MHz step will result with 1 MHz search range for carrier and will often fail for high SR (maybe related to HW design?), in other hand higher step for BlindScan will increase chances to miss low SR transmissions, so it is need to do some compromise on this (2 MHz seems doing the best) or blindscan some ranges twice with higher and lower step.
Probably that's the last my post on this as I see that nobody is interested to improve this which is really disappointing