The site has a working 824 and just converted to ATT fiber, On incoming calls the DTMF digits are not being recognized by the auto attendant 'at times.'
Tested by sending DTMF with handset at interface - Panasonic is OK.
ATT says there is a 'short haul/long haul option in the Panasonic. I can't find it.

Anyone had this issue?

Here is a similar problem: https://sundance-communications.com/forum/ubbthreads.php/topics/168647/DTMF_FiOS_Issue

Above similar problem sounds similar but no resolution noted.
Based on testing I suspect the ATT router but checking just to be sure.

I like my smart phone but sometimes miss the black rotary dial that weighed 5 pounds.

The thread is 8 years old...perhaps things have changed...perhaps not.

Solved by reverting back to analog. ???

That's the way the post sounded...however a lot can change is 8 years and your serenio may not be the same as yours....provider, equipment...software...et cetera.