There is an important thing to mention here and that is if the OP is using MSE now there is no guarantee of how long that itself is going to be supported for use on Win7 PCs.
MS have been been providing contradictory information about this but their initial response was that Win7 + MSE was not going to be supported beyond Win7's EOL (End Of Life) date. Apparently they've since either changed their mind, been persuaded otherwise or that initial information was completely wrong, apparently. In short: everything is still very uncertain.
But from what happened with WinXP there are going to be no guarantees. MSE, or at least older versions, could be installed and accepted daily AV definitions updates automatically for several years after its EOL.
But at some point, mid-2016 I think, the MSE automatic AV definition updates stopped working. It would try to download them, stall at about 66%, retry and then simply stop and report MSE was not up to date. There was no warning from MS about this beforehand and no information provided by them as to why this was happening. That is typical of MS.
It was soon discovered that you could still manually update the definitions by going to MS downloads and getting the latest installer there. But mid-2018 that stopped working too. Again no MS warning or information provided.
However, a clever guy on another forum worked out a solution and provided an installer tool which worked for about 6 months until MS pulled the plug completely and made the definition updates incompatible with the older versions of MSE running on WinXP machines.
So how long MSE is still going to work with Win7 nobody knows at this point. You can be pretty certain MS are going to end support for it completely in the end and MSE users like the OP are not going to be able to return to it even if they do not get on with AVAST or whatever alternative they've tried.