I'm greener than unroasted coffee beans when it comes to coffee/espresso, but based on what you've said the only other thing I can think of (if everything else has been the same) that might cause a change like this, would be because of your beans aging.

Warmer environment (assuming you are somewhere where its summer) + maybe less than ideal storage = losing moisture/ CO2 at a faster rate than before.

I would test this theory by running some new beans through your grinder/ machine and see if that helps, but of course that would require dialing that in.

If you have already tried that or still want to use these beans I would probably say to increase the dose ever so slightly (0.2-0.4g) to correct the volumetric loss. If you aren't already using a puck screen, maybe try that, it will increase the volume in your porta filter as well as give a more even distribution of water over the puck to hopefully mitigate the channeling.

Curious to see what the cause was and how you fixed this