It's more a UI quirk. So I closed a channel and the payment is stuck due to low mining fees.

In the past I have use the RTL UI to increase the mining fee to get it through. However, in this particular case I just left it and after three days RTL's menu to increase mining fees just disappeared and now I have a stuck transaction and no way (in the UI) to boost it.

So I guess I can do a child pays for parent via bitcoin-core to get it through but it's so odd that after three days the RTL option to bump mining fees disappears.