Is my AFCI outlet to blame for a trip when continuing a circuit outdoors due to moisture?
Is this an AFCI outlet or a GFCI outlet? GFCI is more common for outlets. AFCI is normally (but not exclusively) at the breaker. GFCI can be either at the breaker or at an outlet. Either way, the device protects all devices following it (if wired correctly).
My hunch here is that this is a GFCI outlet. While moisture, in theory, could lead to tripping an AFCI device, that is not the normal design. But that is the normal design for GFCI: a little moisture in the wrong place lets some current leak to ground and the GFCI detects that and trips to keep someone from getting zapped.
In most cases, GFCI isnot required for lighting, even if there are receptacles on the same circuit that require GFCI protection. That being said, when you know there is a problem, it makes sense to fix it rather than simply bypass the GFCI for the lighting part of the circuit. Since the boxes look pretty clean, that leaves three likely culprits:

Moisture getting into a light fixture. This can certainly happen - there are holes in the box in the picture. If you test with a basic fixture and the problem does not happen initially, but does happen after you put everything together and let it sit for a day (accumulating drips), then that sounds like a moisture problem. If you have a moisture problem, I would (a) see if you can replace (or properly close the holes in) the box so that moisture can't get in.
Faulty fixture. If you install the fixture on a dry day and the GFCI still trips as soon as you turn on the switch, you may have a bad fixture, the type of problem GFCI is actually designed to catch. That can be due to insulation breakdown in the fixture, a pinched wire or a number of other problems. Replacing the fixture is the solution.
Crossed Neutrals. This is a tougher problem to figure out. This should never happen, but it does. A typical case is if you have a bunch of switches in one box that includes multiple circuits (breakers). If the neutrals aren't kept matched to their hot &amp; switched hot wires, things will likely work fine until you install GFCI. And then they won't work at all.