Context welcome. :) I assume this is due to https://www.mediawiki.org/wiki/Topic:S2gux2za46y9zqsv and having received more than 2000 notifications lately?

Yes, that is correct. See also T227853.

Since I had 1996 notifications "5 years ago" (Can't cut and paste the date) it's likely that some were lost before then, and certainly they have continued to be shuffled off the LIFO since.

Can someone please restore the lost items.

I am neither sure that's technically possible nor that someone will have time for this, to be honest. :-/

Growth team have access to x1 databases. They might be able to find the notification but if it's not there, I don't think there is a way for us to retrieve it.