Material "clumping" when printing
From your initial photos, it looks like the bed level was too high, and there was thereby more material extruded than fit in the space. Even with an "identical" nozzle, the distances involved here are on an order of magnitude (less than 0.1 mm) that you're not going to get identical distance to the bed from one nozzle to another.

Further, as you found out following up, not having the nozzle tightened all the way will affect its height, and allow molten material to exit around the gap. It's always a problem not having your nozzle tightened all the way to make a good seal (I actually had nearly the same problem the first time I ever changed a nozzle), but having the bed too close probably made even more material ooze out at the gap due to backpressure.

Hopefully fixing these two things gets you back to printing right. It might be some work to clean out any material left in the hotend, especially if it worked its way around into the threads where the nozzle screws in. Be gentle if you have to clean that out further, since it's easy to strip the threads if you use abrasive tools, and then you'll be looking at replacing the heater block.