Lightroom Classic sync extremely slow – compared to Lightroom Downloader app

Hi everyone,

I'm currently trying to migrate my entire Lightroom CC library (about 41,440 images) into a new, empty Lightroom Classic catalog.

However, the sync in Lightroom Classic is extremely slow: after more than 20 hours, only about 3,200 images have been downloaded.

For comparison:
On the same system, I also ran the Lightroom Downloader app, which downloads all images in about 20 hours total – many times faster. The app maintains a stable download rate of 30–100 Mbit/s, with peaks up to 200 Mbit/s.

But when I pause the Downloader and activate the LrC sync instead, the download rate drops to below 1 Mbit/s, with only occasional peaks and very long idle times. Sync activity in LrC barely progresses, and it seems to load only 1–2 images at a time, with frequent stalling.

Both apps are:

• Running on the same system

• Using the same network

• Talking to the same Adobe servers

So I can safely rule out any system or network bottlenecks.

I've already tried:

• Resetting the LrC sync cache

• Starting with a fresh catalog

• Creating an LrSync diagnostic report

My question:
What is causing Lightroom Classic to be so severely throttled, when the official Downloader app clearly shows the system and connection are fully capable?

I'd really like to use Lightroom Classic as my central archive and keep syncing from the cloud (e.g., mobile uploads on the go), but at this pace, it's questionable whether the full sync will ever finish.

Thanks in advance for any help or insight!

Roland