Previously if I sent a message it was recorded in recent activity, but recently, as in the last few days I'm not sure any messages I'm sending are being delivered AND no activity is being recorded for the messages.

This coincided with receiving a message from Mingle saying that due to a glitch my account had been limited, but the email said that was fixed. However I'm not sure any messages are being sent as even people I've been chatting to have not replied.

it's very odd.

Most likely you were reported as a scammer.. And system locked you down.. At times you have to wait till they look at the report to determine if the report was false or not if false then they will clear your scammer report and you will be able to send emails..

But before they clear you all your emails to the system looks like a scammer..

Check again to see if you can email and they show up that you sent them .... Ohh it is not a glitch it is the system in place due to sending the same email out to many over and over.. If you send someone and email 5 times and they do not answer you the system will not send anymore emails to that person you just don't know that.. Until they send you a response back you will not be able to have your messaged go through to them..

This is not a Bug it is all laid out in the Help section https://mingle2.com/welcome/help