Despite an old post, a relevant aspect (maybe) can be gleaned.

Stirring properly and following can instructions may have been a part of the OP's problem, but I think moisture contributed to the issue.

The OP said the wood was stored in the garage (in essence, outdoors, cold temps?), yet the work place was a "heated porch". He/she said the wood "... "feels" moist". He/she may not have allowed the wood's temp to acclimate to the work place's higher temp, hence, there may (likely?) had been slight condensation on the wood surface. I assume, quick condensation formed on the can's lid, also, apparently (again, I assume, by what the OP said) immediately after opening.

In the OP's (I assume) colder climate location, plus the garage vs heated porch immediate environment, there may have been a significant temp difference to cause some condensation, despite his/hers generally dry climate. A significant temp difference, from garage to work place, can negate the general dry climate arena.

Op said he/she had used the product, before, with no problems. What might have been the difference in the two work scenarios, circumstances.... Weather conditions, prep conditions, temp acclimation, something else, including can instructions?

Where was the poly stored? Was its temperature greatly different from the wood and/or porch area, also? ...and compare this to the previous "no problem" usage.

Sonny