Dropbox desktop (Windows 10) won't sync while connected to my Cable ISP but will on Verizon hotspot

[robp]

Dropbox desktop v121.4.4267 (Windows 10) won't sync while connected to my Cable ISP.  This started on Friday (4/23)  I've isolated it. 

All from one Windows 10 machine.

When connected to my cable ISP I get "waiting to sync".  I've also bypassed my router and connected directly to my ISP modem via an ethernet cable.  Same "wating to sync".

If I switch my connection to use my phone as a hotspot (Verizon) it will sync.

I've checked with my isp and they are clueless. 

Are there specific ip address associated with the desktop sync that I could ping to trouble shoot?  I'm trying to determine if they are blocking something.

Thanks.

[Rich]

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@robp wrote:

Are there specific ip address associated with the desktop sync that I could ping to trouble shoot?  I'm trying to determine if they are blocking something.

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There are no published IP addresses, but you can find a list of the domain names used by the service in the following help article:

• https://help.dropbox.com/accounts-billing/security/official-domains