why am I intermittently getting this problem…it will print over 50% of the bed as smooth as gloss paint and then “miss” a line or create this mess which then hits the extruder…I levelled the bed before starting
Are you cleaning the build plate? If you are, how?
Get some oil or grease on it and it can affect how well filament sticks down. Increasing the build plate temp a little can also help.
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thanks for your prompt reply…yes I have cleaned the bed with IPA, I am printing with (Creality Hyper) PETG and have found that bed temps of 80 then 70 and extruder temps of 260 then 250 to be the ideal settings
It is not always in the same area
I have run through the various calibration settings in Orca to confirm extruder rates and maximum flow etc. etc
IPA cleans to an extent but evaporates fast and can redeposit oils and not fully clean.
Warm/hot water and plain dish soap are what most recommend with a good rinse and dry with clean plain paper towels. No detergents good for hands with moisturizers, and no cloths that have been washed with detergents with softeners and scents.
But now that you mention PETG, it’s hygroscopic and that can also be a sign of filament with too high of moisture content.
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yes, I am aware of that but it is being stored in an airtight (very airtight!) container in a warm room…APART from that issue the rest of the print works perfectly with super smooth edges and faces etc…
You don’t suddenly go from no moisture symptoms to full on stringy disaster. And what you mentioned about filament moisture mitigation (air tight container in a warm room) says nothing about any drying steps and by itself isn’t adequate for many. What I can tell you is PETG HF I have received from Bambu has had enough moisture to show issues right from the bag.
But I can’t say your issues are moisture or not. Good luck to you.
well I appear to be doing so ! 
If you have a cool room the relative humidity will be say **% if you warm the room the humidity will go down on a meter but in reality what has happened is that the air can now hold more water, so your problem has technically got worse if the room cools the dew point will lower this is the point that the air lets go of the water.
thanks for the suggestion but the rooms are kept at pretty much the same temperatures…and, as I said the filaments are all stored in a sealed box
It makes no sense that it can print around 95% of the first layer (200 x 135mm) as smooth as a layer of gloss paint then “suddenly” develop this problem
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A sealed and impermeable box only holds filament moisture where it was when you put it in the box. If you are using a ziplock bag, those are a little permeable to moisture. They slow down water movement but don’t eliminate it.
You seem convinced your filament is dry. You might want to look through the myriad other posts showing bed adhesion issues here and how moisture was frequently to blame. Wet filament looks dry. You can’t tell it’s wet until you do more than look at it.
PETG is hygroscopic. You need to be on point with drying and storage to get the best results.
And it does make sense that you may only see minor water issues at first. It sounds like you are in a high humidity environment in general if you are running a dehumidifier. I’d bet your dehumidified air is still pretty moist. If the spool printed fine before and now is showing issues, it could be you’ll be seeing even more issues soon.
Moisture trips up a lot of people. You still haven’t said if you are drying the filament but another misconception people have is filament arrives in the bag “dry”. It absolutely does not and can have a range of moisture contents from “prints fine” to “encased my extruder in plastic”.
All excellent points…none of which I am arguing with !
I just re-started and it has put down all the base layers TO PERFECTION and is now doing likewise to the infill… for the record our indoor humidity is a pretty steady 56% so I cant see why it failed previously
What changed between the fail and the success?
The photo you provided indicates issues that have a cause.
Indeed…but what…
The plate was clean, I ran levelling and calibration …can’t see what more I can do