I will go from the top to the bottom from the easiest to perform, to the more difficult steps. Most of those tips will also help when the issue is not directly caused by the mods, but come from the game itself.

You have probably seen this simple tip more than once, but it really helps in lot of cases.
Right click on the UBOAT in you steam library, select properties, local files, verify integrity of game files...

This one is also relatively easy to perform,
go to the C:\Users\[YourWindowsUserName]\AppData\LocalLow\Deep Water Studio\UBOAT. Make sure the UBOAT is not running. Delete the contents of "Cache", "Data Sheets" and "Temp" folders. Do not delete the folders themselves as the game will complain. UBOAT will generate new content of the folders when you launch the game again.

It might happen that the mod files are not downloaded properly or are not updated to the latest mod version, so this might help, although it should be already covered by step #1.

I also usually read the manuals only when something is not working (as most people), so this is probably the right time to check the mod description in detail. I always have Features and Known issues (if there are any) sections in my mods. My mod descriptions are usually quite long read, but please check if the conditions you are experiencing are not actually the intended behavior, or already listed in known issues. Also check discussion below the mod, it might be that someone already had the same problem as you and there is already solution or explanation.

Sometimes some mods do not work together, you might find this information in the mod description or in the discussion below. Obviously if the mod was created for previous version of the game, there is chance, it is not working after the game update. I try to keep the compatibility information always up to date in my mods.

After none of the above helped, the chances are, there is a real bug in the mod, which you can help fixing by providing useful feedback.

You can find the game log under C:\Users\[YourWindowsUserName]\AppData\LocalLow\Deep Water Studio\UBOAT\output_log.txt. Open the file with text editor of your choice and have a look for few things:
Is the mod loading? Do you see some message from the mod? My mods contain messages with [Mod Name] so you can identify them as well as most of the other mods. Mods that only change Data Sheet values will not make any message in the game log.

If you see the mod has loaded, try searching for word "error" and "exception". If you find some, its not yet the win, as the game itself will produce them from time to time, even with no mod running, but it is a good start. In any case, save the log file where you think the bug in the mod happened as it will be useful for the analysis by the mod developer.

One hint to the logfile. It is updated immediately after the game writes messages in the console. Console is quite limited in the span of messages you can see, but you can open the log file while the game is still running with no problems and scroll thru the whole history of messages. The log file will be keep all messages when you close the game, but will be cleared when you launch the game again.

The folders, which contents were cleared by you before, will be populated with new files on the next game launch. Temp folder contains the .dll files compiled from the mods that contains scripts when the game is launched. It can happen that because of some problem with the mod, the game will fail to compile the dll and it will have size of 0kB. Name of the dll should be similar to the name of the mod like magnetic-detonators.dll for example.

Second folder to check is the Data Sheets folder which contains the binary versions of .xlxs files from the vanilla game and .xlxs files from the mods. The files here have .dat extension and their name should give you hint from which mod they come. Again look if some of the files does not have 0kB size.

Bug report with the steps to reliably reproduce the problem is hands down the best one, as the mod developer can analyze situation in detail on its own. Try to be very detailed in description as sometimes the smallest details is what matters. Providing a save game with condition that leads to the bug is also very helpful.

Well that is all I can think about at this moment. In case of problems with my mods, just contact me directly on Steam or on UBOAT Discord after none of the basic tips helped.

salamander