There are several places where the ISA tool interprets texts from Wikidata as HTML without escaping them. This is problematic, because Wikidata labels and descriptions are not necessarily HTML-safe.
Example: go to https://isa.toolforge.org/campaigns/77/participate, then search for the item ID Q43981055 in the “depicts” field. You will get one browser alert as soon as the search results load, and then another one if you select the search result.