I just had a issue with a Roamio basic not detecting an inserted cable card and found it had a bad card slot. Not saying this could be the same as the problem you are had but given it was paired, working and suddenly wasn't able to see the inserted card I would say it's a bad cable card slot. Be careful when inserting the card into the slot, but sure it slides freely horizontally and in no circumstances apply any vertical pressure to the card or card slot esp any pressure downwards were the card's pins make contact to the slot connectors.
Be sure the green plastic ejection knob is only moved horizontally, don't be tempted to pry it up when manipulating the card. I urge you to keep a close eye on this as once your Roamio goes past it's 90 days, it won't be a free no charge fee to correct their poorly designed engineering mistake, if you suspect it's bad, I would urge you to insist that Tivo replace it before it's warranty expires. Mine broke a few days over it 3 month warranty and tivo wouldn't budge in offering any grace.
Yes, some cable cards can be difficult to pair but I'm taking the firm position that this different style of card slot in the 4 tuner Roamio is a poor, defective design. I wish I could go into more details but I awaiting Tivo to replace mine under it 1 year warranty coverage which costs $$'s, after I have mine settled, perhaps then I can elaberate more about this. Needless to say, I'm not impressed with the quality of TiVo's newest hardware.....
TiVo Roamio Pro
TiVo Roamio Plus (3tb)
TiVo Mini (three)