Data upload not possible | Stuck at "a few seconds"

From my own experience, I can report that installing Debian on the SD card and using an external SSD for data storage has caused me many problems. Better is to install Debian OS directly on the SSD and store your data there as well and not use an SD card. For me it has brought significant speed benefits. Before that, the upload speed was a disaster. I suspect it has something to do with the shared cache. I hope it will help you.