With all due respect, this alone kind of raises a flag. Your entire mission (dare I say your livelihood) hinges on the quality of that card. The fact that you don't know off of the top of your head exactly the brand and model suggests the purchase of just any old Best Buy MicroSD card with enough capacity to complete the mission. But let's move on.
SanDisk Extreme Pro. Settle for nothing less. Purchase 2, as they're not infallible. I've RMA'd 4 or 5 of them over the years. SanDisk always sends a free replacement. Even when I crashed a drone and physically damaged the card in the crash, they replaced it. I was frankly quite surprised.
I generally use 128GB cards, but DO use my 64GB cards for small-medium size mapping missions.
That's very, very low and a lot of overlap. Any low-medium quality MicroSD card would be overwhelmed.
Though this isn't really part of your problem, I recommend using Shutter Priority. And at that altitude, I would probably lock it in at 1/1000. If I recall, the X3 has a fixed aperture, which is real disadvantage for mapping (IMHO). A high shutter speed will insure against motion blur, which is your worst enemy in the mapping game. I normally set ISO @ 200, but since the X3 has a fixed aperture, I imagine Shutter Priority adjusts ISO on the fly to compensate for changing lighting conditions. Honestly, the Inspire 1 is not the bird I would use for Mapping. But if you're only doing the occasional job, and that's the bird you have, it certainly is a robust platform that you can rely on.
I've been using MapPilot for years. Agreed, it's not without its problems. I use a legacy version 4.1.7, which is not perfect, but is relatively stable and reliable. These bugs have been minor inconveniences. Nothing that couldn't be worked around. I've never had to re-fly a mission because of these occasional bugs. So I continued to use it for years.
I would be interested to know which version you have and which bugs/issues you're experiencing.