all small sections of the carbon lacquer has gone white in colour and the lacquer has flaked away as exposing the bare carbon paint underneath !
Looks like something (water/product) has compromised the clear coat and reacted causing it to degrade. I wouldn’t worry about it, a bit unsightly maybe but I wouldn’t have thought it’ do any harm. if you’re really worried then you could maybe rub it down and apply another topcoat of lacquer .
Either way I’d say this is a good lesson about making sure you don’t trap moisture and ‘stuff’ under anything protective you put on the frame. Could have been way worse on a steel frame if you’d trapped a load of moisture against a bit of downtube with a few chips or scrapes through the paint 😉
If the rest of the frame had done this too (ie: where you hadn’t put something over it) then you might have a cause for complaint, but putting a non-breathable covering over the tube, trapping water, muck and god-knows what against the lacquer for months at a time is asking for trouble. I’ve seen people do all kinds of damage to finishes with aggressive cleaners and things in very short time periods, let alone trapping stuff there under a rubber tube for a while.
Even if you didn’t use cleaners and stuff, water isn’t just water, think about all the crap in road muck, and how acidic/alkaline mud and whatever else gets flicked up from the trail can be.
If you feel the need to add protection then Helitape is the best option, it’s not that expensive, lasts ages, is self-healing to some degree and you can add extra layers if you feel you need more protection, it also sticks pretty well and doesn’t let moisture in behind until the edges start to peel (which takes ages) and then it’s pretty visibly obvious so you can keep an eye on things too.