It's the acid used in the bleach that causes the gelatin to denaturate. The permanganate doesn't counteract that while the dichromate does.
Having said that, you have several options:
1) use the permanganate at 18°C;
2) use a glutaraldehyde hardener in the first developer and a permanganate bleach;
3) use dichromate;
For the fogging step: you can use a dithionite fogging redeveloper. I'm working on it. There's this household chem "Super Iron Out". I'm told it will work but as of today I still haven't found the right concentration. 15g/l seems too little, fog is uneven and it yields muddy gray instead of solid black.
Stannous chloride must be used in an acidic buffer (acetic acid/acetate) otherwise it won't work.