First, yes you can downgrade to previous firmware — you can either go to the release history:
and find the firmware you needed. Or you can go through the commit history and identify the commit point that corresponds to the firmware you needed and check out that version.
Second, I don’t believe the weather algorithm issue is particular to firmware 2.1.7. Did you check the Last Successful Weather Call time stamp (this is available in Weather Diagnostic dialog). That time stamp shows the most recent weather query result. If it’s empty or not within the past hour, that means it’s not getting the weather query result. It could be that something on your network is blocking the return packets to your OSPi.