ITV HD has recently changed it’s forward error correction settings which makes it a bit less robust than usual. Some older Panasonic and Sony kit is unable to view at all. Not seen any issues at all with Humax kit, but your dish alignment may need adjusting or as you say the lnb is on the way out. If you move the problem box to one of the known working points does it then work OK ?
ITV SD is not affected so is it ITV HD you have problems with ?
STV HD currently uses the old paramaters, tuning using non freesat will show if it’s the FEC that is the issue.
11068 V DVB-S2 8PSK 23000 2/3