Builds occasionally hanging for 45+ minutes on "starting to extract cache" step

Our site uwalumni.com has a very large cache (~5.3GB) but 98% of the time it completes the cache extraction step in 7 to 9 seconds.

Twice in the last five days we have looked into the site’s deployments to see why page changes weren’t yet on the website, and found that builds were hanging on the “starting to extract cache” step. On 4/17 a build started at 12:15 and I discovered it hung and canceled it at 12:51. Then again this morning (4/21) a build started at 8:49 and I did not notice that it was hung until 9:54.

We do have a long max deployment time set on our site (might be 2 hours, I can’t remember), because when we have to do do full builds without cache, they can take a long time. But I wish there was a way to see that the cache extraction is stuck and cancel the build when this happens.

Are there any tricks or workarounds that might help with this? Or any clues at what might be causing this to happen occasionally?