Slow Upload over WiFi while download speed normal

I have three phones where the upload speed is terribly slow (below 0.1MBit/s) over WiFi. Download speed is normal. Upload over mobile data is fast. Only when using WiFi, upload is slow. Tried in different WiFi networks. When trying other devices (phones and laptops), upload is fast using the same WiFi network. Only thing in common for the affected phones: Used them in Egypt on vacation. But did not install anything, so don't know what could be the cause. Using Android 13. Any advice?