ICP-OES 5800 Chromium falling out after couple hours

Lately, I've been having issues with my Chromium. It calibrates fine at first, but over the course of the day the recovery in my CCVs steadily climbs until it becomes unusable. This used to happen only occasionally, but now it's happening daily, regardless of tubing replacements, cleaning, standard prep, or any other factor I can think of.

In troubleshooting, I've figured out that on day when it behaves,  my midpoint of 500 ug/L comes in at ~10,000 c/s. On days when it becomes a problem, the same midpoint can be anywhere from 5000-8000 c/s. I'm thinking that it's counting low at first during calibration, then recovering after, but for the life of me I can't figure out why. No other analyte does this. Blanks remain okay, at least.

If it helps, I've set Cr at 267.716 nm, Axial viewing.

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