Any idea? It’s a floorplan for an event, so not sure what the original drawing was done in.

Print out and on screen via acrobat lines are there, but when opened through illustrator they are all gone?

what version of Illustrator? Are they there if you zoom in?

no, not there at all, latest version 2017, it also happend in the previous version, as I’ve just updated.

My colleague tried it and all his lines were too thick and all there?

just went to VIEW > CPU PREVIEW and they’ve appeared!

Open file and flatten transparancy

The last two versions of illustrator make objects magically disappear from time to time. They still exist but they’re just temporarily not visible. Options to resolve this:

a) Pan the object off screen and then back on again.
b) CPU Preview (as above)
c) Outline view (cmd Y)

There’s a similar issue with snapping to objects.As it seems related to GPU preview it could just be a problem with some graphics cards. It’s crap but par for the course for Adobe bugs, I don’t hold out much hope of it being fixed for the next 4 or 5 years so it’s worth knowing how to work around it.