I saw someone post this in an online forum earlier. Mostly they were getting decent advice: needs a setup, might need a truss rod adjustment, etc. Someone even thought to mention that this could be the result of improperly installed strings (not on the saddle).
Strings flat on the fretboard has actually happened to me just a few years ago. The seasons had changed and I hadn’t picked up that bass in a while and bam: strings flat on the board. This can happen because guitar necks are made of wood and wood reacts to temperature and humidity. It’s nothing for your neck relief to increase or decrease by a few hundredths of an inch because of environmental factors. It’s to be expected, really. It’s why they come with adjustable truss rods in the first place.
And, like many other problems, it has a familiar solution: see to the neck relief, then the string heights, pickup heights and intonation. Although, if your bass had been well set up before, maybe the only thing it will need is a crank or two on the truss rod. Once you’ve put the neck back where it was, the other things will be correct again.