Sorry, my bad. I thought everyone spent black friday testing their christmas lights and finding out that they need to buy all new ones.
Are these regular, AC-powered light strings? Or is there a power supply?
Regular cheapo outdoor light strings, connected to a few heavy duty outdoor extension cords. The strings wrapped around the balls (which were new last year, and the problem began last year) are these.
There’s probably some leakage around one or more bulb sockets due to moisture.
I concur with others that you should just plug them into a non-GFCI receptive.
Update on this - I used a meter to measure the wattage and it was around 800 watts for the whole display, so I can’t use the transformer **beowulff **suggested. I bit the bullet and bought all high-quality LED replacements. If for some reason THOSE still trip the GFCI, I actually should be under 300 watts at that point (it’ll be around 150W) and can invest in the transformer next year.
I’ll do one more update to let you know if the higher quality lights did the trick. Thanks for all the advice!