Adhesion Issues

Up until now, I was getting really good adhesion of PLA to my heated glass plate. In fact, it was so good that I would have to wait for parts to cool before I could peel them off. For some reason, the adhesion has suddenly turned very poor, and I can't figure out why. I'm using the same heat setting, the same spool of PLA, and the same isopropanol to clean the glass. What could be causing this issue? Has anyone else had something like this happen? Could it be a humidity problem (it's gotten much warmer here in Atlanta the past few days)?

Thanks!

If you have printed bed springs they may have deformed so that the bed sits a little lower. Maybe you changed bed temp, or the thermistor's thermal conductive path to the bed changed so the delta between the thermistor reading and the surface temp is different. This might cause the expansion of the bed to be different and slightly farther away from your nozzle than before.

I've honestly never diagnosed this sort of problem in a systematic way before, I just turn the screw on my Z opto end stop a little bit until they stick (or unstick) again.

Humidity does have an affect on PLA, it absorbs water from the surrounding air.

Could still be a machine problem though.

Have you checked that the bed thermistor is giving accurate readings?

I haven't checked the thermistor yet, but for whatever reason I started getting good adhesion again yesterday. I honestly have no idea what was causing the issue. It just started adhering again.

Probably is the humidity. I only have problems with PLA adhesion once the relative humidity gets to about 75% and above. Then it becomes a real hit and miss affair.
I'm in sunny (very wet this time of year), Queensland, Australia.

It was definitely a humidity issue. It happened again this morning. I was getting great adhesion yesterday, but this morning it wouldn't stick for anything. I came to the realization that it rained all last night and I had my window open all morning to enjoy the cool post-rain temperatures. I closed the window and let the A/C dry the air out for a while, and now it's sticking like a champ again. Lesson learned.