Hi
@inthedark_06 Welcome to the dark from 2am in Victoria
How many prints are you putting through your developer; also, how long is the developer out in the trays in open air? I'm with ooze on this one, it does sound like developer exhaustion, assuming you've been consistently developing your prints to completion (i.e. ≈1min. for resin coated paper and 2-3min. for fibre base).
I follow the recommendation to use separate working solutions for stop and fixer for paper from that used to develop film, but reusing them on both won't cause any fading or contrast dramas.
All of your chemicals will have capacity limits stated by the manufacturer either on the bottle/packet or on their website. They tend to be quite cautious in their estimations, but following them and keeping track of how many sheets of paper/rolls of film you've put through your working solutions eliminates a variable in your process.
I hope you find the cause of the problem you're having and can return to getting good results as soon as possible.
Have fun!