Ok, so I've moved all my coins to Electrum app through private key, and everything was fine and I was going to attempt a double spend to clear the previous tx attempt, but VERY SUDDENLY, Electrum is displaying that i am attempting to move the coins so i am facing the same problem as when I had my coins on Airbitz. It's indicating an unconfirmed transaction from Dec. 17 originally, only this time, my receiving address is finally indicating an unconfirmed tx.
It's almost as though the broadcast never worked in the first place (receiving address never picked up an unconfirmed tx) due to low fee...but now that the mempool is clearing up, it's rebroadcasting again?? Would this be the case? It's such an old tx though.
I guess what happened was, like others said, only a few nodes had that transaction still - it is old. When you used Electrum, it synced, picked the tx up and rebroadcast (that's what happens when your Electrum client is connected to the network). As long as you keep it connected, it keeps rebroadcasting.
The earlier broadcast worked, that's why the tx is in the mempool, and will continue to be there as long as you're broadcasting. If you're also the recipient of these unconfirmed outputs, in the same wallet, which is what you seem to suggest, then you can help this confirm via a CPFP tx.
There's some help on how to do this and calculate the fees, just Google. Basically, you use the same outputs to make another spend (the child), including a fee enough for both the child and parent (the unconfirmed tx). If a miner picks it up, both txs will confirm in the same block.
It's quite easy to do this in Electrum... just only choose to SPEND:
1M2gjWLikYqKxx4aKoKTgh5FBv1rXSNtWd - 0.07962544 BTC
and
37nMuvRCD7Gdk1Pyc2i47kg9b3cLE4bzw5 - 0.308577 BTC
you can post further if you need help.