I had this problem as well. It may have started after the latest MacOS update, but I can't say for sure. Regardless, I noticed this in the log file:
2021-06-11 15:51:17,091 - DEBUG - [MainThread] cura.OAuth2.AuthorizationHelpers.parseJWT [114]: Checking the access token for [https://account.ultimaker.com/check-token]
2021-06-11 15:51:17,299 - DEBUG - [JobQueWorker [2]] UM.Mesh.MeshData.calculateNormalsFromVertices [556]: Calculating normals took 0.00214385986328125 seconds
2021-06-11 15:51:17,496 - WARNING - [MainThread] cura.OAuth2.AuthorizationHelpers.parseJWT [123]: Could not retrieve token data from auth server: {"errors": [{"id": "dec451e5-b44e-457c-9aef-bc6a198ad3b1", "code": "invalidToken", "http_status": "403", "title": "The given token is invalid.", "meta": {"error_type": "AuthError", "url": "https://account.ultimaker.com/check-token"}}]}
2021-06-11 15:51:17,502 - DEBUG - [MainThread] cura.OAuth2.AuthorizationHelpers.getAccessTokenUsingRefreshToken [61]: Refreshing the access token for [https://account.ultimaker.com]
2021-06-11 15:51:17,813 - DEBUG - [MainThread] cura.OAuth2.AuthorizationService._storeAuthData [250]: Attempting to store the auth data for [https://account.ultimaker.com]
2021-06-11 15:51:17,817 - DEBUG - [MainThread] cura.OAuth2.AuthorizationHelpers.parseJWT [114]: Checking the access token for [https://account.ultimaker.com/check-token]
2021-06-11 15:51:18,116 - WARNING - [MainThread] cura.OAuth2.AuthorizationHelpers.parseJWT [123]: Could not retrieve token data from auth server: {"errors": [{"id": "0be11182-6748-4790-8c93-b60dc848d01c", "code": "invalidToken", "http_status": "403", "title": "The given token is invalid.", "meta": {"error_type": "AuthError", "url": "https://account.ultimaker.com/check-token"}}]}
Once I saw that, I removed the following line from the cura.cfg file and that seemed to fix it:
ultimaker_auth_data =