Made a payment today to chipmixer. Got a session key. It was showing a legacy address (like old version of chipmixer used to show.)
I used tor browser + tor version of chipmixer.
Have you used old Tor v2 version that is now obsolete and it's not using Segwit, or new Tor v3 with new segwit addresses?
I just checked that old version website of chipmixer is still opening with warning message that it will soon become obsolete.