We have had the exact same problem but only on Microsoft based VM's. Upgrade to newer PV-Tools fixed it.
The problem did not occur on Linux VM's
I never experienced such issues, even with Windows guests, that didn't had the latest PV drivers installed. But that's not to say, that you shouldn't upgrade to the latest PV drivers for your Windows guests. Some Versions of those have had real bad issues…
Forgot to mention that the guest is a linux vm (oracle linux 7)
If you can reliably reproduce this issue, I'd say you are in for some interesting analysis on your guest's system. First of all, you will want to perform some tests and see, whether this issue is independant from your OVS hosts, that is, if this issue arises at both ends.
If that is the case, you will have to peek into your guest OS and see, what it is, that makes it choke: CPU, RAM, I/O. Get a baseline for your guest when it's working fine and compare that to when it's running slow. Then try to figure out, if you can correlate that to issues with the host (OVS). As I said, I never experienced such a behaviour, when migrating my guessts between equally loaded OVS hosts.