Half of the "groupIds not available" log messages, roughly 60k requests per day, are being made for impossible maps on Wikidata's Special:BlankPage. An example URL is https://maps.wikimedia.org/img/osm-intl,13,36.814892,-5.744377,310x180.png?lang=en&domain=www.wikidata.org&title=Special%3ABlankPage&groups=_205a9df43a110cb2362515b6d3674c0071e3433f .
These image links are made when browsing a Wikidata entity page with maps, for example https://www.wikidata.org/wiki/Q513
Note that due to this bug, map thumbnails will not have annotations (such as the coordinate marker) on no-script browsers.
The fix is very simple: we need to fill the title parameter with the entity name. The mapdata API already serves these requests correctly. For example, here the title has been supplied:
https://maps.wikimedia.org/img/osm-intl,13,27.988055555556,86.925277777778,310x180.png?lang=en&domain=www.wikidata.org&title=Q513&groups=_61b46232823592e723c88ef29f5e45429366e567 . Note that the revid parameter should also be included.