Situation:
After adding stations from the subway (1 lvl MashUnderground) to the train route, this train in FAT mod is placed on page (54) (the number may change)
while the pages are occupied: 1,2,3,53,54.
The intermediate pages (4-52) remain blank.
Pages 1-3 are occupied by trains that have never been to Underground (as it should be).
Pages 53,54 - trains that have ever been in the Underground. They remain on these pages even after Underground stations are removed from the route.

Save/load game does not help.

example of a train route:
-"Oil storage" (ground) (loading)
-"Gates to the subway"
-"Oil storage Undr" (underground) (unloading)
- "The gate from the subway".

Mod versions:
The FAT Controller: 5.0.7
modMashSplinterUnderground: 1.1.38

Yandex Disc directory with screenshots (may be help): https://disk.yandex.ru/d/AbKABgZPjk-t_g

Debug Info:
After moving train: normal_surface -> underground or underground -> normal_surface: the number of trains increases by 1. (
(train adding in end_of_triansList). after reverse surface movement record in list not deleted (train info = nil) and new train record is created.
If use more than 10 trains, during 1 hour, trains count stay > 1000 and EmptyPagesCount > 100.

used: game.print(trainCount)
control.lua. line 856. (after line trainCount = #trains or 0).

In standart game train explorer train count is normal.