I tried to import my on-chain wallet in BlueWallet by filling in the 24 words. It did not succeed. Also this procedure does not succeed: https://openoms.gitbook.io/lightning-node-management/technicals/restorelndonchainfundsinelectrum.
The resulting wallet in BlueWallet or electrum is empty, while the wallet in the dashboard holds satoshis an shows past transactions. Also I can send and receive with this wallet. There are no channels in the pending state. So this is worying: if something goes wrong, my seed will not work to recover the wallet.
@DarthCoin pointed out there is probably something wrong with the seed.
What can I do? It is important to have a working recovery procedure. Is it possible to create another wallet to fund channels with? Or should I close channels, send the bitcoins to another wallet and start over with a new Umbrel installation?