Waiting for close usually indicates connectivity problems to the peer. For coop close you need to communicate with the peer.
Try manually connecting in settings -> Lightning Network -> Show Lightning Peers -> +.
Discussion
Thanks for the response.
My Blixt wallet is connected to 4 peers. If I press + I have the menu "Connect to lightning peer", asking for node URI. If I type in the node public key of one of the nodes in the list I get an error message saying I am already connected to the peer.
I suspect it's the low fee in sats (less than 1500 sats) that is causing the tx not to be mined. I see RBF is active on the tx so I might have to bump the fee up.
My Blixt LN channel was finally closed after ~5 weeks. Normally it used to take only a few days.
If it is possible to request a fee-bump feature for closing channels in the Blixt wallet, that would be a brilliant addition when the mempool is crowded.