Hello,
We can recommend trying to adjust the following setting for a known possibly related issue with upload speeds and checking if the issue persists:
1. Start your virtual machine.
2. Right-click on "Start" icon ->.select "Device Manager".
3. Expand "Network Adapters".
4. Right-click Parallels VirtIO Ethernet Adapter -> click "Properties" -> go to "Advanced" tab.
5. Locate the property, "Offload.Tx.LSO" -> set its value to "Disabled".
For additional information, please check the following article:
https://kb.parallels.com/en/129589
Please let us know the results.
Looking forward to hearing from you.
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