This might be one of those cases where I’ve not used my legacy bank in such a long time that I might be slightly wrong with how some banks are displaying these now. But in the case of RBS (NatWest) you have your ‘available’ balance and your actual balance.
Your pending payment remove from your available balance but you are still allowed to go over this as long as your actual balance is high enough.
At Monzo we hide this balance behind the scenes so while payments are pending you still get the benefits of interest (not being charged OD fees, etc) but you can’t spend this money.
Tesco’s terminals are coming to Monzo asking if you have enough money in your account so we set that amount aside then they are collecting the payment in an incorrect way leading to a second presentment. Literally as @SouthseaOne has said the app is different in how it processes payments and personally I haven’t had any issues with it either (although I also have never had a duplicate presentment despite using Tesco as my local store)
We are always looking into these issues and working with Tesco, Mastercard & WorldPay to try and make sure that no one gets these issues in the future.
I know it might seem pointless but if you report it to COps when it happens we might not be able to help straight away but it really helps our teams know how big an impact this issue has and we can use this to push for this to be fixed as soon as possible with Mastercard. 
edit: I’m double checking with our engineers the specifics about Monzo Plus/Premium interest I will update this post when I have a clear answer