Is there a pattern to where the gaps are happening? Like are they always where the beginning of a layer starts printing or are they interspersed throughout layers? I recently had a similar problem with my K1 and some random filaments that were a few years old where the start/end points of my layers had holes, almost like the start of the extrusion was lagging behind the movement or the stopping of the extrusion was happening prematurely. I never really figured out the core problem because I just switched to vase mode because it worked nicely for the model I was printing. But I thought about playing with my retraction settings in case I was retracting too much or adjusting my nozzle temp in case these rolls just weren't flowing when melted like they used to (but it sounds like you've tried that already). And I know it's a bit cliche at this point but you might want to try drying your filament especially if you're hearing pops from the nozzle when it's printing.