@Kevin_Z 

Its Archer C4000 and its running the latest firmware. Drive is WD My Passport 1TB.

Tried disabling media sharing and everything. All sorts of combinations and partition types. Formatted several times. Eventually i made it work by doing the following

1. Format my external to MacOS Extened Journaled

2. Created a Spark Image (NOT spark image bundle) as MacOS Extened Journaled on the drive(i had to make sure its smaller than my capacity. I have 1TB external drive so i made the spark image to 800GB)

3. Share my network drive and then mount the spark image from the drive. Time machine feature is disabled on Archer. So i am using the capability of Archer4000 to read MacOS Extened Journaled partitions.

4. Point TimeMachine to use the mounted spark image for backup. Seems like its working fine, was able to create a 250GB and incremental are working fine.

The only downside is that each time i reboot i have to connect to the network drive and then mount the image. Probably you can do this from terminal on startup.

Please let me know if you need more details, i can make some screenshots with my current settings if anyone needs it.

FYI: there will be multiple reasons of the router restart, but it was SSD power consumption in my AX73 + 1TB SSD via USB3 + Time Machine.

Some SSD can consume more power than HDD. See Re:Problem with TimeMachine using AX73.

For all users with this issue, my scenario has changed.

Now, backups seem to complete successfully sometimes, however every few weeks, I receive the message "the identity of the drive has changed", and it asks to create a fresh backup, which fails. Incredibly frustrating, and again dissapointing that this router seems to not have any updates or firmware follow ups for years. The objective of buying the router is having network-connected backups for the two systems in the house, and it won't perform that simple function despite being advertised as specifically for that purpose.

@dalexander 

So, I am having the exact same issue with the router restarting. However, I am using an Archer AX3200 router. I have a 6TB WD Elements Desktop drive plugged into the USB port and whenever I start the back-up, once it goes into "preparing the back-up," the router restarts. SUPER frustrating. My wife's Windows machine backs up to it with no issue. I have the drive partitioned, 3TB Mac OS Journaled and 3TB NTFS. I was just on with TP-Link's support and they had me send them a video of exactly what happens with the lights on the router and my computer screen during the backup attempt. I haven't heard anything yet, but will update if I hear anything.

My AX73(JP)'s restart issue has been fixed by the latest firmware: Archer AX73(JP)_V1_211125.

AX73 + Time machine + 1TB SSD (MBR + exFAT) are up and running for three weeks so far.

The random restarts don't happen anymore, but that's because Time Machine says that the drive identity has changed every once in a while, so it has to start from scratch every few weeks.

I don't even try to do network-connected Time Machine backups anymore, because even if they work for a day, week, or month, eventually they stop and have to be started all over.