Thanks for the compliments, and I'm glad the video gave you some information that might be useful.
I feel very badly for you because of your paint issue, but it sounds somewhat familiar. My brother worked really hard to convert the Revel Starsky and Hutch Torino into a replica of our dad's "Super Value Package"-equipped car that we had since I was born, and kept until 1991. We all loved that car, and he did a tonne of work on the kit.
He painted it with some oil silver and some Tamiya red (for the vinyl top). After the Future was on, he dried in in a dehydrator (standard for us) and then he noticed, a bit after that, that it was all cracked. The paint looks like it had spiderwebbed, but not that finely. To me, it looks like little worm tracks in the car's finish.
The same thing happened to me when I used Tamiya green for a custom Omni I built years ago. It was great when I was done, but a couple of months later, I noticed a similar issue of cracking in the paint.
I've never had the Tamiya polishing compounds chemically attack the Future, and this is what I think has happened:
1.) The Tamiya paint over which you put the Future may not have been totally, chemically dry. Putting Future over it prevents it from outgassing, and can cause problems.
2.) Your Future was likely not totally dry. I have sanded right through Future to the paint below, and in surprisingly short order, if the Future isn't TOTALLY dry. That's why I bake it a couple of days, lightly sand it until you can smell it again, then dry it (in the dehydrator, always) before trying any more sanding.
Even if it seems dry on the surface, Future can be "wet" underneath. It takes AGES to dry, and until it is dry, there's always a threat of something like what you had happen occurring.
If Future isn't BONE DRY all the way through, it will tear very easily.
It will be tough to recover your roof, for a couple of reasons, but it can be done!
A couple of things:
1.) If you use Acrylic paints (incl. Tamiya) then make sure your thinner has Future in it. I've found Future bonds to itself really well, and makes paint very tough, even though it slows overall "through drying" time. I use a 1:2 mixture of Future and 99% Isopropyl Alcohol to make airbrush thinner. it works on all kinds of acrylics, and is the only thinner I've found that works well for Model Master Acrylics.
2.) If you use Acrylics, use Model Master acrylics (MMAs). Tamiyas (and some others) are "acrylic", but they have a very reactive carrier. You can smell it; a Tamiya paint smells "chemical-y", but an MMA just smells a bit like some kind of house paint. It's less toxic smelling. That means it's more chemically neutral, I've found.
MMAs have other advantages, too. If fortified with "blow" (what I call my Future-alcohol thinner) they become very hard. They also don't react with themselves or other paints, unlike Tamiyas. Also, they don't change colour when airbrushed or hand-brushed, which makes them ideal for touching up.
Also, like you've seen, Tamiyas that weren't shot with "Blow" tend to have some issues getting along with Future. If Future is in the thinner, then the Future will help bond the paint to the gloss coat.
A better way:
I've found the Aqua Gloss to be the best. It is TOTALLY chemically neutral on all paints I've seen, and, when heated, dries SUPER FAST. It's also SUPER HARD. It can also be used as airbrush thinner, but it's not as "thin" or fast-drying as "blow-shot" paint.
To recover your roof, I can only suggest this.
1.) make sure all the paint is really dry. Get a dehydrator if you have to. Bake it for like a week+ at 42 degrees Celcius (about 113=ish Fahrenheit).
2.) Apply some Aqua Gloss (AG) if you can get it. Apply several coats of Future (lightly, and separated by drying sessions of about 8+hours in the dehydrator PER LAYER) if you can't.
If you use the AG, go moderately heavy, bake for a few hours, then go really as heavy as you can. Bake for another 5-7 hours and repeat.
After 2-3 days (not overnight, but like, 15h/day) in the dehydraytor. Don't take it out even when you're not running it. Also, put a few small bottles/jars of water in the dehydrator. They'll absorb heat and help to moderate the cool-down a bit once it's turned off.
3.) Now try sanding the roof, as I did in the video.
I hope it will work out for you man, and that my rather long-winded explanation helps out.
Let me know how it goes!