“while some users report that, recent posts in the thread from other users say they have done transactions above £1,000!”
presumably on transfers over 1000 people have funds to cover it , why would you try to transfer more than you have in your account - unless you do it mistakenly
- seems to be quite low limits - for some - if you have more than the amount in the account that you want to transfer
maybe its down to Liquidity and overdraft offerings/risks ? 
I have 10K daily transaction limit in Monzo - so its presumably not a MasterCard limit - does anybody have differing limits - lol not that I have that much in my Monzo
and obviously wouldn’t be allowed to transfer more than my account balance