Looks like Huggle is using deprecated functions to call the API:
dom sep 9 01:52:50 2018 WARNING: API query (revisions): Because "rvslots" was not specified, a legacy format has been used for the output. This format is deprecated, and in the future the new format will always be used. dom sep 9 01:52:50 2018 WARNING: API query (main): Subscribe to the mediawiki-api-announce mailing list at <https://lists.wikimedia.org/mailman/listinfo/mediawiki-api-announce> for notice of API deprecations and breaking changes. Use [[Special:ApiFeatureUsage]] to see usage of deprecated features by your application.
(note: MCR stands for Multi-Content Revisions, I think this is what the API is complaining; in any case the rvslots parameter is mentioned at https://www.mediawiki.org/wiki/API:Revisions so if it is not MCR it might be something else that needs to be looked upon - thank you).