Macbook Pro sync errors only on WiFi - it works when connected to a different computer's WiFi

Running v202.4.5551 on 2 Macbook pros and 2 iMacs; longtime user with no problems until now.

One of the Macbook pros is new (an M1) and is unable to complete sync after desktop app installation. It will start OK but then stall after 5-10 Gb. This is selective sync for about 200 Gb of files that I want to maintain (and sync) offline. No sync issues are reported, and large files (10-20 Gb) that aren't on dropbox download quickly. (Running ~100 Mb/s).

This laptop is on the exact same home network with the other Macbook pro (with an intel chip) and both iMacs; there are no firewalls or proxies, and the other 3 computers are syncing just fine, running the same version of the app. Both Macbook pros are running Sonoma 14.5, and configured identically.

I tried the usual fixes: uninstalling/reinstalling app, advanced uninstall, fixing permissions and links, and syncing to an external SSD instead of the internal SSD, all to no avail.

I opened a ticket with support, was told that "it looks like we're consistently getting some errors indicative of an underlying connection issue", and was advised to unlink/remove the Dropbox folder from the app by signing out of the account, then relink with a new folder and path. That didn't work either.

What has worked, just in the last 2 hours is, instead of using the laptop's WiFi connection, using the WiFi connection on one of the iMacs, connected to the laptop via thunderbolt bridge. So...there's something about the laptop WiFi connection that doesn't play well with the Dropbox app. 

I realize this seems like maybe more of an Apple than a Dropbox question but hoped someone here with some Apple expertise might have a helpful suggestion. Thanks.