I got the same problem and I'm using RatePage 2.14.0, MW 1.41 with docker.
I sent pageratins query request and 'ratepage' POST api request(edit token included) with javascript and the server returns 'internal_api_error_Error' in both cases. I tried running update.php with force option, but it has no use.
So I send the query request again, but this time I send it through URL and I got the message:
Exception caught: Call to undefined method MediaWiki\\User\\User::getEffectiveGroups()
...
Error at /var/www/html/extensions/RatePage/includes/Rights.php(39)\nfrom /var/www/html/extensions/RatePage/includes/Rights.php(39)\n#0 /var/www/html/extensions/RatePage/includes/Api/RatePageApiTrait.php(105): RatePage\\Rights::checkUserPermissionsOnContest(stdClass, MediaWiki\\User\\User)\n#1 /var/www/html/extensions/RatePage/includes/Api/QueryPageRatingProp.php(30): RatePage\\Api\\QueryPageRatingProp->processParams(array, DerivativeContext, RatePage\\Api\\QueryPageRatingProp)\n#2 /var/www/html/includes/api/ApiQuery.php(695): RatePage\\Api\\QueryPageRatingProp->execute()\n#3 /var/www/html/includes/api/ApiMain.php(1935): ApiQuery->execute()\n#4 /var/www/html/includes/api/ApiMain.php(912): ApiMain->executeAction()\n#5 /var/www/html/includes/api/ApiMain.php(883): ApiMain->executeActionWithErrorHandling()\n#6 /var/www/html/api.php(95): ApiMain->execute()\n#7 /var/www/html/api.php(48): wfApiMain()\n#8 {main}
It seems User class has been changed since MW 1.39.0+. In 1.35.0 release note, it says:
The following methods of the User class are deprecated: getGroups, getGroupMemberships, getEffectiveGroups, getAutomaticGroups, addGroup, removeGroup, getFormerGroups, getAllGroups, getImplicitGroups, addAutopromoteOnceGroups. Use the new UserGroupManager service instead.
Also, this talk exists: Error: Call to undefined method User::getUserEffectiveGroups() on Extension talk:AccessControl (mediawiki.org)
PS: when I visit 'Special:RatePageContests' I can see a debug log:
Deprecated: strlen(): Passing null to parameter #1 ($string) of type string is deprecated in /var/www/html/extensions/RatePage/includes/Special/RatePageContests.php on line 76