Ender-3 V3 SE problem with first layer not sticking

Ender-3 V3 Printers Creality Ender-3 V3 (Regular)
1

I have had some good prints and no problems with the first layer until very recently.
I have levelled the bed using the built-in levelling program and also set the Z offset as I have done in the past without any issues.
I have tried a few times now to do a print, I used several known good print files and all of them have detached after or during the first layer.

I am using a brand new Phantom PET plate and ABS filament.
Previous prints with the same setup have all been perfect and the finished print just falls off the plate as it cools.
Now the first layer wont stick down at all,

I had an unrelated issue that may have caused some problem. A roll of filament had a tangle and stopped feeding, causing the job to fail and then the build up of plastic from the bed melted around the nozzle and the silicone boot came off the nozzle. Since that time I have had the problems.
Not sure what to look for now. I have relevelled the bed using the built in software and also checked the Z offset, and using a new plate.

2

ABS on an open air printer? You want an actively heated closed printer. ABS loves to warp, an open printer is not what you want to be printing ABS.

3

I have the printer in an enclosure, I have had no problems previously, all prints big and small have been perfect.

4

I have fixed it.
I re-levelled the bed again and after doing that I moved the Z down to zero position. I then placed a piece of paper between the nozzle and the bed and found it was very loose.
Then I adjusted the Z offset so that the paper felt quite tight but not enough to stop me being able to pull it out.
After doing another test it printed good again.