It happens one day and the next day you get a perfect transfer. Even in air
conditioned environment. I faced this problem some time ago but it seemed to
have solved by itself somehow. My suggested explanation: I think is has to do
with the surface tension of the plexi, which is too high, and probably also the
drying speed. The print makes crackling noise when peeling it off. And this is
probably due to the way you clean the plexi before, i. e. which detergent you
used, how much and how well you washed the plexi afterwards. The early printers
used (resin) coated papers, glass plates or celluloid foils which all had to be
waxed to get the right surface. Hanfstaengl also used a subbing layer with their
stripping tissues on polyester which was called 'microwax' coating.
So if I had been more desperated in the past I might have tried the wax method
on plexiglas. What if you solved a little bees wax in a solvent, pulled the
plexi through it and, after the solvent had evaporated, polished the plexi with
a soft cotton pad?
Or you just wait for better weather... ;-)
Good luck,
Klaus
p.s.: What if it were (very) little airbells trapped during the transfer? I
always take my hake-brush and under water wipe over the surface of the transfer
paper before combining it with the plexi.