First of all - it will not appear in regular mod list now, so we need this list (marked with red)
You open it and select there Barotrauma 40k

And Than you MUST restart the game in order to have everything working properly.

Sometimes mod can gone from any lists. Thank steam automod for it. Usually it takes less than 5-10 minutes but sometimes it can gone for few days like in first days of January.

For some reason very often after mod update it disappears from mod list. Try to verify game files so it can download mod properly.

If you have error with missing files try to verify game files. Usually it helps and steam stops being monkey.

Not possible. Disable ALL mods then hit "Apply" button, then select 40k in content package list.