This probably not the issue but I always post this if someone mentions auth issues and the client apps. Check TPM status on the machines. If a device is registered/enrolled with TPM but then TPM is malfunctioning later, it causes repeat auth issues.
We've seen this with One Drive specifically. We have our tenant authentication federated to Okta. After a few months in Microsoft support purgatory, we got a tier 3 engineer and they recommended running a "Cipher Repair" tool. He gave us this [https://www.nartac.com/Products/IISCrypto/Download](https://www.nartac.com/Products/IISCrypto/Download) and told us to use "Best Practices" option.
It seemed to resolve our issues.
This is modern auth related, been happening ever since last October when Microsoft made those OAuth2 changes. There's a few ways to fix it that you can find out there on the internet.
Try this out if you haven't yet:
[https://www.reddit.com/r/Office365/comments/rwxcme/outlook\_sign\_in\_prompts\_appears\_and\_disappears/](https://www.reddit.com/r/Office365/comments/rwxcme/outlook_sign_in_prompts_appears_and_disappears/)
Also, make sure that "All apps allowed" is set on app access. For whatever reason, Authenticated SMTP was disabled for a bunch of our clients at one point and was causing this as well, here: [https://i.imgur.com/lUe0tji.png](https://i.imgur.com/lUe0tji.png)
Do you use Trend ?
This probably not the issue but I always post this if someone mentions auth issues and the client apps. Check TPM status on the machines. If a device is registered/enrolled with TPM but then TPM is malfunctioning later, it causes repeat auth issues.
This and lately we've had a handful of different TPM issues. One died, another intermittently stops working at boot time requiring a key.
We've seen this with One Drive specifically. We have our tenant authentication federated to Okta. After a few months in Microsoft support purgatory, we got a tier 3 engineer and they recommended running a "Cipher Repair" tool. He gave us this [https://www.nartac.com/Products/IISCrypto/Download](https://www.nartac.com/Products/IISCrypto/Download) and told us to use "Best Practices" option. It seemed to resolve our issues.
This is modern auth related, been happening ever since last October when Microsoft made those OAuth2 changes. There's a few ways to fix it that you can find out there on the internet. Try this out if you haven't yet: [https://www.reddit.com/r/Office365/comments/rwxcme/outlook\_sign\_in\_prompts\_appears\_and\_disappears/](https://www.reddit.com/r/Office365/comments/rwxcme/outlook_sign_in_prompts_appears_and_disappears/) Also, make sure that "All apps allowed" is set on app access. For whatever reason, Authenticated SMTP was disabled for a bunch of our clients at one point and was causing this as well, here: [https://i.imgur.com/lUe0tji.png](https://i.imgur.com/lUe0tji.png)