That's not Mycelium's fault. According to Blockchain, we have almost 170k unconfirmed transactions in the mempool. Meanwhile, the fastest and cheapest transaction fee is currently 950 satoshis/byte[1] - which is pretty sad. You either need to pay an astronomical fee for fast confirmation or wait some time before seeing your transactions coming through.
The mempool right now:
[1]
https://bitcoinfees.earn.com/Its not good, I think that's why devs need bch or B2x to increase the block size of btc, fastest transactions with low fee.