I'm pretty sure I heard somewhere that some people lose all their mods when Train Simulator upgrades to a new version (like TS18 to TS19), but I want to know if this is true.
Depends on what you mean by "mods" You shouldn't lose any content, so routes, assets, consists etc You shouldn't lose any 3rd party content or reskins, but if you have to do a validation of the files as part of the update then this CAN cause some resets of enhancement packs (such as the AP HST enhancement packs), so I would suggest backing up your asset and content folders prior to upgrade day, just in case What MAY have issues is any 2rd party plug ins (things like raildriver support, RailworksEnhancer etc), because the way that train sim works might be different between the versions, but this is up to the 3rd party to solve rather than DTG to accommodate One other thing to remember is that 2018-2019 is a special case when it comes to updates. Because TSx moved from solely 32 bit into 32 and 64 bit versions of the game (which would speak to 3rd party content differently) there were probably more issues than there will be in a general revision update such as this time round, so hopefully less overall issues in 2019-2020 than last year where a lot of stuff keeled over, some of which STILL doesn't work properly (such as 64bit raildriver support where they don't seem to have worked out the key mapping or macros as yet)
If your modding is done outside of the .ap files you will be okay. If you modify within the .ap then any file vreify or update to the asset will overwrite your changes.
Most people don't change the *.ap file as there is no point. The Game looks first for files outside the *.ap file and then inside. Peter
If they are not working have a look on AP's website for updates - once purchased you get free downloads each time it's updated. https://www.armstrongpowerhouse.com/index.php?route=information/information&information_id=12 Peter