Is it still stalled? That actually sounds very normal. This article relates to mailbox moves, but the same concept applies:
https://techcommunity.microsoft.com/t5/exchange-team-blog/resource-based-throttling-and-prioritization-in-exchange-online/ba-p/608020
You can wait it out or stop/ resume it or recreate it, but in the end, 365 will throttle connections as it see fits.