Sounds like you have signal issues on the frequencies used by those channels - which happens to be the same. There's a few other channels on the same frequency that you can check to help verify this theory...
Quest Red, Zee TV, Crime&Inv+1, BBC Alba, CNBC & E! (All SD) - plenty of others, but this should help prove it.
Always worthwhile restarting the affected box to eliminate software gremlins. If that fails to resolve, I'd suggest swapping your boxes around - this will then help ID whether it's the box or your internal cabling at fault.
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