I've been having a strange issue that hopefully someone can help me with.
I've had this L1 for a year or so, and initially worked well and I was pulling really great shots, best shots of my humble home barista life. The lever hype was real for me.
Then I had a thermosyphon issue, and per Reiss's instruction I performed the group sleeve descaling service. This fixed the thermosyphon problem, but after that, I started getting bad channeling, but only in the later half of the shot. The first 10-15 seconds were good, with even coverage of the basket and single stream, then it would fall apart badly and make undrinkable shots.
No change in coffee or technique. I don't switch coffees much, either using Klatch WBC or Counter culture Big Trouble. 16-17g in 17g IMS basket ground on NZ and WDT. I've tried with no puck screen or with Sworks thin metal screen with no difference. I've changed the seals to new Cafelat seals as well as the Londinium greaseless seals. I changed out the shower screen as well.
I'm now fully out if ideas. Would greatly appreciate any insight!

Do you have a way to measure temperature and pressure at the puck?
That might provide some useful insight.

Blends often change seasonally. Are you seeing the change with both coffees?

It might be worth cleaning your grinder, if you haven't already tried that.

Unfortunately I don't have a Scace or similar device to measure temperature and pressure. I thought maybe the seals were failing, causing fluctuation in pressure, but I've since changed the seals twice.

Jeff wrote:Blends often change seasonally. Are you seeing the change with both coffees?

It might be worth cleaning your grinder, if you haven't already tried that.

I'm seeing it across the board with all coffees. I don't think I've cleaned the grinder since this started. probably a good idea to do anyway, but not sure how that would help.