The issue of disappearing airports at landing has been discussed so many times on the official MSFS forum, and it's a known issue that can happen everywhere, caused by having reached the maximum number of Simobjects in a scene, which can't be more than 1000 overall.
The most common causes for surpassing the limit, is too much AI Traffic, especially if using AI Injection, so you need to keep the number of AI lower.
If you use FS Traffic, there's an option to remove Ground services for AI, which will also help a lot when keeping the number of objects down.
