Mail forwarded to me is getting lost!

Since the early 1990's I've had a mail forwarding account from ACM.ORG that everyone uses to mail me, and it forwards the mail to my current account (a comcast one for years).  Recently I discovered some mail is NOT getting through to my comcast box.  I checked with the acm.org managers and they confirmed I have all mail filtering turned off on their forwarding server, they also said they have heard other reports of mail from their forwarder getting lost going to comcast/xfinity.

In my case, not ALL forwarded mail is getting lost.  For example when I mail my acm.org account from gmail or my work address, it gets through.  What is really alarming is that some important mail is NOT.  The big one being mail from California's Franchise Tax board (the California IRS).  I talked to them directly and they confirmed they were getting no error reports and the mail was being sent to the right address, it was just silently vanishing.  This was multiple emails lost over several months time from different senders at the FTB.  I ran some tests to make sure their mail wasn't in the spam folder or anywhere else...it was just disappearing without a trace.

When they (internally) changed my e-mail from the acm.org one to my .comcast.net address, it started working.

There has to be some way to fix this, if mail from other government sources isn't getting through it could cause me a lot of trouble!

Specifically, my email at ACM is my_name@acm.org and at xfinity it is myname@comcast.net.