Link with PayPal so you can see forthcoming payments that are going to be taken from monzo account by PayPal but are going to be delayed
Several times I have bought via PayPal using my monzo account and it doesn’t instantly get taken out but takes weeks so by the time it gets taken out of my monzo account I have spent the money thinking it was available as it wasn’t showing as pending in monzo
The ability to link them and get more accurate balance data
You need to pay with your card and then it’s instant.
It happens with both instant bank transfer and as a card payment and from what I’ve read it happens to a lot of people
If it’s coming through weeks later it’s because you have paypal set up with a direct debit.
This 
Link your debit card instead of having a Direct Debit to your account and it will go through instantly.
At least, mine does 
it could be possible you have “pay after delivery” on which usually take the money 14 days after you have paid for it
No, considering this also happens on instant items like games on eShops / Steam etc
Another PayPal user here, using card for payments. Always goes through straight away for me.
Use your card through PayPal, then it will be instant. As @Revels said above, you are paying using your bank account - this means it is a direct debit.
I’ve got a direct debit, and sometimes use pay after delivery, so I’ve set up a PayPal pot and I stick the sum I’ve spent in there and point the direct debit to the pot. I’ve also got it set up to dump my change in there, so it builds up a little extra.
It’s useful to have both linked imo.
You can get creative with your budgeting to buy things before you get paid with direct debit.