[Sticky] FSUIPC7: WASM crash and how to prevent (presets stop working, lvars stop updating, etc)

UPDATE January 2026: FSUIPC7 versions 7.5.6 and later, containing WASM v1.1.0 or later, contain changes that make the WASM CTD a lot less likely to occur, so please update to this version if you think the WASM has crashed.
Also, Asobo have finally confirmed that this is due to a bug on their side, and has now been fixed for MSFS2024 in SU5 Beta. No fix yet in MSFS2020.

An issue has been identified that can cause the FSUIPC7 WASM module to crash. When this occurs:
    - presets will no longer work
    - lvars will not be updated
    - FSUIPC can hang when restarted

It has been reported that this occurs only when using complex aircraft AND complex scenery, and is more likely to happen after an aircraft change. If you experience any of these systems, please confirm that the WASM has indeed crashed. To do this, firs exit MSFS. Then open your FSUIPC_WASM.log file, located in your WASM persistence area which is:

For Steam installs, in the following folder under your user account:

    AppData\Roaming\Microsoft Flight Simulator\Packages\fsuipc-lvar-module\work
For MS Store installs, in the following folder under your user account:
    AppData\Local\Packages\Microsoft.FlightSimulator_8wekyb3d8bbwe\LocalState\Packages\fsuipc-lvarmodule\work

The last line in this file should be an 'END OF PROGRAM' line like the following:

Mon Aug 19 09:46:17 2024  [ALWAYS]: <=============================== END OF PROGRAM ===============================>

If you do not see that, then the WASM has crashed.

The crash seems to be an MSFS issue that has been reported. If you find that the WASM is crashing then you can try tuning the WASM via ini parameters to prevent this. You need to disable continual lvar scans by setting

      LvarScanFrequency=0

and if setting this it is also a good idea to tune the delay of the initial scan, by increasing the value of the LvarScanDelay ini parameter (the default is 8 seconds). Suggest, for complex aircraft, you use:

      LvarScanDelay=15

Please see the Advanced User guide on setting WASM ini parameters. You should set these in the FSUIPC_WASM.ini file in your WASM persistence area, not the one in your Community folder. If this doesn't yet exist, copy the one from your Community folder to the WASM persistence are location (details in the Advanced User guide) and then edit removed link

If the WASM isn't crashing, then something else is causing your issue. Please enable WAPI Debug level logging (Log->WAPI->Debug) and Event logging, as well as WASM Debug level logging (via the FSUIPC_WASM.ini file) and the next time this occurs please exit MSFS, create a support topic and show me/attach both the FSUIPC7.log and FSUIPC_WASM.log files.

John