I updated to the latest Craft version.
This error shows under the field in entries (backend):
This field’s target subfolder path is invalid: {slug}
I checked the field and there is no {slug} tag at all.
Fronted shows images fine, but with that error I cannot update my entries.
In whatever Section you're getting that error in, you've got an Assets field inside of Matrix (or possibly SuperTable) and that Assets field has “Restrict uploads to a single folder” set and you've got a dynamic subfolder path setup for it.
In that dynamic path, you're using {slug} when you should be using {owner.slug}.
From the docs:
Note that if you are creating the Assets field within a Matrix field, the source element is going to be the actual Matrix block, not the element that the Matrix field is being created on. So if your Matrix field is attached to an entry, and you want to output the entry ID in your dynamic subfolder path, you would type {owner.id} not just {id}.
