I left mine in my unheated and uninsulated garage in New Jersey over the winter, where it froze several times, and then used them just fine this summer.

I don't know if there is a difference between freezing cold from time to time and freezing continuously.  My guess is that if you shake the containers up a bit so they're mixed in case anything separated out, you'll be fine.

   Please please remember to do a test batch before you use any epoxy that might have been compromised. A test batch will show if it is still good and potentially save you a very messy cleanup of epoxy that has decided not to harden.

   Please please remember to do a test batch before you use any epoxy that might have been compromised. A test batch will show if it is still good and potentially save you a very messy cleanup of epoxy that has decided not to harden.

Epoxy doesn't separate when frozen, it crystallizes. No amount of mixing will dissolve the crystals back in. Instead, you need to dissolve the crystals by warming the epoxy. A hot water bath works nicely.

Laszlo