Emails vanish or are not being delivered

I'm having two consistent issues- people respond to my emails nad I can see them on my Xfinity phone app but not on my desktop when i log in, or people tell me they send me replies to my emails but I never receive them. My mailbox isn't full and they aren't in my spam filter. I had one critical email show up on my phone app this morning and by the time I got home and logged into my desktop Xfinity email it had vanished from both. This is my work email and the issue has got to stop. What is going on?