Cannot upgrade last S stand in INN

After this update, I upgraded S stand to M stand in INN, but I found that the last S stand could not be upgraded. I don’t know if it is because of the game mechanics.

I expect: work as designed

For example only m and x is also possible at bigger airports

Yep this is as planned. It’s the stand you start out with, and prior,to the update you couldn’t take it to a M stand. Just a little tip, if you haven’t already upgraded the cargo stand to M, it will disappear. The stand does remain in place and useable. Just no markings.

Not every stand is upgradeable… i learned that during internal testing. So yes this is intended not a bug.

This is not only in INN airport, even in BRI and PRG. I’m assuming they intended this so that you are guaranteed to have atleast 1 (or more) stands for just 1 plane size so that you can land that size aircraft instead of landing queue.
Again, I’m not sure but I like this feature

Not every stand can be upgraded (on any airport).