If you are still trying to refresh your portal metadata using cache invalidation handle https://nottherealportal.microsoftcrmportals.com/Cache.axd?Message=InvalidateAll, stop it. The caching invalidation mechanism significantly changed and the legacy methods are no longer appropriate or supported.
Instead, remember the advice you gave your auntie when her computer was slow? That’s right, turn it off and then back on.
Navigate to CRM Admin Portal > Applications > Portal Add-On > Manage then turn your portal off, Update, turn it on, Update.
That will restart the application and refresh metadata (note: the first page load after that could be excruciatingly slow so, if it’s a production system, choose your time wisely).