Has your living space gotten cooler, or are you opening a window that you weren't before, or have you started running AC or a fan near your printer? The ambient air temperature and especially drafts will affect the cooling rate of the plastic, which will contribute to shrinking. If you can, block the area around the printer and/or get an enclosure for it.
Are you cleaning your print bed regularly?
Have you run actual temperature tests with this particular filament?
Have you releveled your bed?