Today I finally recovered the Bitcoin cash from a Mycelium wallet that I used a few years ago.
I have found the important information here and here.
This article deals with small but essential variations to the above articles (BIP39 instead of BIP138 and different derivation code).
This is what worked for me:
transferred my Bitcoins (BTC) off of the Mycelium seed I was recovering BTH from (I have read about some red flags in Electron-Cash and have not evaluated whether they are real or not)