You may want to peruse this thread from back in October, it’s long but it had a lot of community tips and suggestions. https://forum.bambulab.com/t/transparent-petg-basic-any-tips/
However, for this case I can clearly see what the issue is. PEI just doesn’t work that well with PETG. However, here’s a little trick I learned. If you’re stopping your print early because of a lousy first layer, try letting it print a millimeter or two. I found that when I had issues with a crappy first layer, sometimes just letting the layers mount on top for certain models worked just fine believe it or not.
When I experimented with Transparent PETG, I had no end of trouble using PEI. I was able to get it grudgingly to stick by using adhesive. But I struggled much of the time exactly like what your photos showed.
Ultimately, I was able to create consistent and perfect results by going back to the old-school of using a smooth plate with adhesive, I used hairspray a smooth plate but glue stick also did the trick, both Bambu and Elmers glue stick. Using hairspray, I coated it like I was painting with spray paint. I used thin even coats and let it dry first. This is admittedly overkill but if you want to get great adhesion AND get optically clear results, that method paid off.
I tried five different plate surfaces but what ended up working best was the standard Bambu two-sided Engineering/High temp plate. It really didn’t matter which one. My bed temp was 65.
The plate I used wasn’t pristine by any means. In fact, it was pretty marred up with scratches, but as you can see by the image below, it looked almost brand-new when coated with just two layers of Hair Spray(Aqua net).
Note that I first washed the plate under hot water in the sink and then scrubbed it with a brand new sponge to ensure no contaminants transferred to the plate. Once that was done, I used a copious amounts of Windex to ensure a complete oil-free surface before spraying. This last step is not needed if you don’t see any blemishes after hair spray. The nice thing about hair spray is that if you don’t have a clean surface, it will show in the reflection. You’ll see oddities. In fact, on my plate, you can see it where I handled it. I zoomed in and increased the contrast to make it more obvious. The camera doesn’t capture it but the human eye easily can see it.
When restoring heavily contaminated plates, these are the two items I used. The Dobie is the gentlest but the Scotch-brite green side is good for getting excess filament that PETG sometime leaves behind. Just go lite at first and then inspect your plate so that you know you’re not damaging it.
https://www.amazon.com/s?k=Scotch-Brite+Heavy+Duty+Scrub+Sponges
