One email address in my contacts disappeared. It does not pop out automatically anymore when I spell the first letter.

I checked in my red list if I had misplaced it but this address was not there either.

I still can write to this person and she will receive my emails. However I do not receive her emails anymore.
I tried to trick the system by emailing her through the same account with a second account I put with the
new system since Microsoft suppressed the links accouts. Same thing: she will receive my email but I do not receive

Can anyone help me to fix this problem.
Thanks a lot.