You have given us rather little information about what your logic looks like. For instance FreezeThaw has various hooks to allow you to put logic in the freezing and thawing process. Are you using those? If not, then I would suggest giving Storable a shot.

However I would wonder whether your frozen string is getting long enough to not fit in whatever database field it is going into. Check whether that is plausible. (For instance report the length of the string going in and coming out. If they differ, you know what it is.)

If neither of those two naive guesses helps, you really need to create a minimal test case. Do you have a reliable interaction that does it? Can you script that interaction on the command line? Once you get to that point, try to start cutting out steps, and keep on going until you have the shortest case you can that reproduces it. After you get there, you are going to be in a much better position to figure out what it is.