Microsoft have had issues for a week or so now with Sharepoint & OneDrive in their O365 suite. Access issues, speed issues, all intermittent.
The Powerapp I have been working on has been really slow also, I put it down to the tie in with Sharepoint, however checking service health today all appears fine:
Using developer tools its seems the invoke calls to https://europe-001.azure-apim.net/invoke are causing long delays, but no issues reported in Azure service health either.
Hopefully its just a hangover from the other issues they have been having and all will be back to normal tomorrow.