I am also having the same issue with the Fenix with this scenery as of today with the latest update.
***Update***
Did a full reinstall of KIAH on the FSDT installer and that has fixed the problem for me so far.
Hi DefiantPrawn, have things still been working since your reinstall? I have tried removing all addons, reinstalling both FSDT IAH and GSX completely. I have narrowed my issue down to GSX. I even run into an issue where taking off from HOU, flying over IAH on a departure, I get a CTD as soon as I get into close proximity to IAH, even when FSDT IAH removed completely. So I am crashing even with default IAH scenery it seems now.
Tested it now, can't see any problems, this is with the latest Fenix installed, which also called automatically the jetway through its automation. VGDS works, showing GSX is working normally as well.
Virtuali, I went ahead and attached a log from one of my flights were I was not able to load into IAH. I initially thought it was the scenery but It seems when I disable GSX, I can get into both default and FSDT IAH without issue. Then as soon as I enable GSX, the sim freezes. It doesn't really crash, just locks up and becomes unresponsive. I have to kill it in task manager. If I try to load into IAH with GSX running, I can get in all the way maybe 1 in 10 times, but the other 9, I get the same locked up sim before I can get to the airplane. If it is one of the times I can get into flight all the way with GSX running, I either get a freeze or CTD after a minute or two. Also as noted above to DefiantPrawn, I can even take off from HOU, GSX running, all is good. Then as soon as I get anywhere close to IAH (default or FSDT IAH, either one) then I get a full CTD. Hopefully the attached log might help see what my sim is doing? If there is other logging or anything specific I can do to help you please let me know and I will get it to you. Thanks for your help

p.s. I am getting theses symptoms in the Fenix A319/32/321 after the BFU, the iFlymax 8, and the PMDG 777-300. I don't seem to get this issue with the current version of the CRJ though. I was able to land at IAH one time without issues, but as soon as I pulled up to the gate, the sim crashed.
***UPDATE*** 09/05/2025 - 9:13PM CT
I jumped into the sim in the Fenix A320 at C4 with FSDT IAH and GSX both. Loaded in just fine, no issues. All seemed well. Restarted Couatl via the GSX menu and as then CTD. Log from this most recent event is attached now as well called "09052025_Coutal.log.txt" and additionally added the couatl64_boot log as well, called "09052025_couatl64_boot.log.txt"