what is the url of your repository? if it on bitbucket / gitlab or github and it is being accessed through your linked account, try unlinking and re-linking that account. as under some circumstances the oauth token used to access the repository may have been revoked.
Thanks Vangroover - I managed to avoid this issue by moving to a public Git Repo (the previous ones were private). I'll try this as I would prefer the Git repo to be private if possible.
Thanks for the answer.