It seems the container began leaking or the desiccant got saturated.

This one only got pulled down to 15% briefly before popping back to 20% every night.  The last successful drying in February stayed at a constant 9% in temperatures only reaching 58C while dew point went negative.  The desiccant pack was wet but not mush like the truly expired ones.  Surprising that the desiccant would saturate right when the filament went in the sun, but it might show how important heat is for drying filament.

Replacement desiccant continued to saturate in short order, with dewpoint not getting significantly below 0 & humidity not getting below 15%.  The 3.3L rubbermaids were the most expensive, topping $7.   Now they're $11.

Smaller desiccant containers which can be reconfigured for horizontal & vertical packing might be the best.  They're not allowing the lid to seat securely so it might be time for a 2.5 gallon rubbermaid.

New desiccant improved it slightly, but still nowhere close to the -35C dewpoint it should reach.

Noted with the latest desiccant bottles, it gets saturated next to the paper while the rest of it stays dry.  So there's always emptying it out every single day or going back to the pure paper towel bags.   Emptying it out every day returns water to the container.

The ultimate desiccant trend is just dumping it in the bottom of the container.  All the electronicals would have to be moved to the top.  Experience has shown it's possible to manually keep the desiccant on the bottom of a ziploc bag separate from the filament. 

All the scotch on the inside degraded.

The mane task is increasing the surface area of the desiccant.