Hello Jodi,
I have followed your instructions and the only filter was the only one set when everyone was being plagued with spam and specific emails were set to be moved into the Spam folder. I have since deleted this filter and all the email associated email addresses. I am going to action the same for all accounts in case it's this rule that's the cause yet spam was going into the spam folder and not just vanishing, so it's very puzzling as to what the cause is.
I know the emails are going astray when people call me to enquire I have not answered their emails. I have watched online when they send it again yet doesn't arrive. I have since archived the OST and PST files and created new ones yet emails are not arriving.
I do know that Edinburgh Council have implemented a block on email addresses that have been reported as PWNED, as I have to confirm other addresses to get around that system; also blocks emails with numbers, https://haveibeenpwned.com/ is where anyone can check. This is where various companies have been hacked and not the end user at fault.
Kind regards,
Morrile