Steps to reproduce:

• the huwiki sandbox and edit it with VisualEditor: https://hu.wikipedia.org/wiki/Wikip%C3%A9dia:Homokoz%C3%B3?veaction=edit
• click Cite
• enter https://444.hu/2020/07/08/tettestarsai-nem-usztak-meg-olyan-olcson-mint-kaleta-gabor as the URL (random example; happened with various URLs) and press Generate and Insert
• press Edit on the template dialog
• select "szerző" (author) from the TemplateData field list, enter something and press Apply
• press Edit again
• select "kiadó" (publisher) from the field list

The new field will appear at the bottom of the dialog, with no info etc. as if it were a field with no TemplateData information. After pressing Apply, the field won't show up. Reopening the dialog, it won't be present in the field list (neither in the existing, nor in the available field group). Trying to add it manually will similarly have no effect. Switching to wikitext, one can see that the the field has not been added.

One has to reinitialize VisualEditor (e.g. switch to source editing and back) to get the field to behave normally.

Since Citoid tends to omit author and publisher for many Hungarian media URLs (and puts the corresponding information into other, less relevant fields instead) this can get quite annoying.