There were two problems here.
One was the cold metal and the outside air was about 70. The next problem was fast reducer. With cold metal its the worst thing you can use unless the outside air matches the metal temp because at 70 degrees air temp and 50-55 metal temp the outer coat of the base is going to flash real fast and the bottom part of the base is dormant.
The giveaway? Fish-eye eliminator helped! ONLY by slowing the clear down to let the solvents escape. You could have done the same thing with a shot glass of very slow reducer.
So how will you know/? If you re-clear it the solvents are now in the clear instead of the base, so the first coat of clear will go on fine and its the second coat that will blow up.
What are the odds that the last three cars he had this problem with all had contamination problems. What are the odds it was cold metal on last three cars?