I'm surprised a person with all your experience is having this problem. But I'll still explain the relevant workflow for sake of others too. (Actually, I have a little voodoo doll of Bob, and jab it with pins every time he goes to the mounting press.)
The tissue transition has worked so identically for me that I can't even tell the difference functionally. There is a tiny bit of visual difference to the sheets, and of course different labeling. These tissues actually achieve full bond under cooling after being hot pressed. Once I pull the print/tissue/mountboard sandwich out of the press, its's immediately placed under a thick sheet of heavy plate glass for five minutes or so, for sake of the cool-down phase. It has to cool under pressure.
One also needs to be aware of the ambient humidity conditions when doing this kind of work. You want things dry on your work session days, and need to briefly pre-dry both your print just before mounting them together. But that can be overdone, especially on an unexpectedly dry or warm day, or due to too much press "dwell time", especially under such conditions. In other words, if the mount board or print gets pressed for too long, or gets too hot for one reason or another, it's actually counterproductive in terms of successful bonding; hence the potential risk of loose corners or edges.
These Drytac Trimount tissues need to be pressed 190 to 220 F for around 45 seconds; don't overdo it, or the tissue bond might fail at the corners, just like with previous Seal Colormount. (That is the dwell time for my own big 500T press; your own individual prescription might vary from that a little).
One more technicality - once in awhile, some of the silicone from a badly worn out sheet of release paper can actually transfer to the print or board, and inhibit bonding. That's a rare issue; but one should always use new release paper or board if the old sample is beginning to look ratty or splotchy.