Ripples on First Print Layer - BIQU B1

[Mags999]

I've been getting what look like ripples or waves across my prints at the first layers.  Sometimes it gets "evened out" with successive layers, often not.  This is a behavior I've never seen in over two years with my Ender Pro 3.  Anyone ever seen this?  I've checked all the first layer speed, layer height and fan settings.  Nothing obvious seems amiss, but I'm sure I'm missing something obvious.  Thank you.

[BIQU info]

Hello, please clean the Z-axis screw and see if the situation improves.