GFCI is tripping intermittently

Hello!
I was recently given a spa, an Outback Savannah (Outback branded Hydro Spa 910) using a Hydro Quip CS6230. I had an electrician come out to hook up the electrical. He used a Eaton 60 Amp CH Type Spa Panel (Model #CH60SPA). When he first hooked it up, the breaker would trip immediately. After looking at the manual, I noticed he had wired it wrong so I had him come back and fix it, and everything worked great.

When the weather started to get a little bit colder, the GFCI started to trip intermittently, only when I was at work, or sometimes overnight. I could never get it to trip manually when I tried. This would happen every couple days, maybe once a day sometimes. Fast forward a month and a half and now temperatures are below freezing. The spa trips at least once a day, and now I am able to trip it manually when I turn on Pump 2, but only sometimes. Sometimes it stays on and works great. Other times, pump 2 will turn on and after about 10-30 seconds, the GFCI will trip. Sometimes I can turn it right back on, and sometimes I have to wait a few minutes. I have never been able to manually trip it with pump 1 on high. I have a suspicion that this is somehow temperature/humidity related but I'm not sure how I would test that theory. I suppose it could also be pump 2, or a wire related issue. Maybe even something on the board? A capacitor or a fuse going bad? Should I try to swap out the GFCI with a new one?

Other things to note: I put a new heater element in when I got it and that works great, I'm using a used pigtail/whip(the wire that goes from the GFCI to the hot tub encased in the thick gray flexible (conduit?)) I got this from my father that had previously used it in a hot tub installed around 10 years ago. The wire is 6 gauge (it has the two power wires, a neutral and a bare ground, and it looks like the same wire the electrician used to hook the GFCI up to my main breaker. I have opened up the spa cabinet and there is no moisture near pump 2. There is a tiny bit of water near pump 1, but I couldn't find the source, just a very small leak somewhere in that area. The control box is bone dry.

Do you have any ideas? I do have a multimeter and am tech savvy so I'd be able to test anything needed.

Thanks!