try updating fastboot on your computer. I believe older versions of fastboot cause errors. I had a similar issue where after going back to stock my keyboard wouldn't show emoji. My issue was fixed by updating fastboot and then flashing back stock software.
What This Is
This is a personal project to get Lineage OS running on my Pixel 3a XL. I got the idea to build it from this thread of the Pixel 3a . It seems to suffer the same short comings of the 3a version in the link provided.
What's Been Tested
So far tested on T-Mobile (at least) with Nano...
gotcha, it's cool. I pulled out one of my laptops and got a build environment setup. Since I haven't built lineage in a long time I'm having trouble as well. Got Breakfast bonito going with no errors but cant get proprietary stuff without errors. maybe we can exchange notes.