What the heck is causing this?
I've cleaned my print bed, tried with and without painter's tape on the bed, run multiple calibrations, and I still get a weird pattern in the first layer. In the darker parts of the first layer shown, there is pitting in the underside and tiny tips lifting on the top side. But the rest of the first layer is fine. I've run out of ideas. 
RE: What the heck is causing this?
My guess would be that the plate is not clean. The darker areas are where the first layer has not adhered. See boiling water an Dawn washingup soap for a solution.
RE: What the heck is causing this?
As towlerg mentioned - clean your heatbed - looks like your heatbed is a MK2S version - so no way to put it under (boiling) hot water. So use a Scotch Brite cleaner and use the hard / rough side and go in circles over the whole heatbed, then use isopropanol alcohol to clean. Is this a print in PLA? (and before you uset PETG?)
Second: It looks like as your nozzle is little to deep. 1st layer on a MK2S can be tricky.
Best regards, Clemens
Mini, i3 MK2.5S, i3 MK4, CClone (Eigenbau)
RE: What the heck is causing this?
o no way to put it under (boiling) hot water.
Sorry for rubbish advice, didn't even know a Mk2 printed directly on bed.
RE: What the heck is causing this?
On the MK2S (and before) there is the PCB and directly on there is the PEI-sheet.
Best regards, Clemens
Mini, i3 MK2.5S, i3 MK4, CClone (Eigenbau)
RE:
Thanks everyone. My confusion is coming from the fact that the pattern appears in the same place, even if I clean well with a scrubber and alcohol or put a fresh coat of painter's tape on the bed. With the fresh tape, cleaning should not be an issue since it hasn't been touched. I was beginning to wonder if maybe it was a problem with a heater zone in the bed. I'll try with very hot water and dish soap and see if it makes a difference. I'll also adjust my nozzle up a tiny bit and see how that goes.
RE: What the heck is causing this?
Are you printing from SD-card or are you using Octoprint. If you use Octoprint you can use BedLeveling plugin to get an idea how level your bed is.
Best regards, Clemens
Mini, i3 MK2.5S, i3 MK4, CClone (Eigenbau)
RE: What the heck is causing this?
AS your heatbed/PEI is apparently unusable at the moment, have you considered using a fresh kitchen sponge with pristine green Scotchbright, to scrub the surface with dishsoap and hot water, and see if the results are any better... (Some folk prefer to use 1000 grit wet and dry paper to restore printability... )
Regards Joan
I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK
RE: What the heck is causing this?
If you've already tried cleaning the print bed and running multiple calibrations, you might want to check your printer's settings to make sure everything is set up correctly. It's also possible that your printer's nozzle is clogged, which can cause issues with the first layer of your print.
RE: What the heck is causing this?
It could be a mix of things, like the height of the tip, the temperature, and how fast the print is going. Change these and see if that helps.