So, things that could be causing an issue, corrupted Flash installations due to using th updater system and not a full uninstall/install.
Conflicts with another application such as another firewall/antimalware or incomplete removal of a previous AV system.
Are Windows Firewall and Windows Defender shutdown, is there any other resident protection running?
Flash based malware is all over the net but getting 3 machines infected is unlikely but possible.
Kaspersky itself could well be the issue, I gave up using their suite long ago as it crippled my machines,their support tried long and hard to sort things out but in the end I just cleared all reference to it from the registry and went with Avast AIS and all the problems were gone.
Personally I would go to the Kaspersky forum and ask for their help. I know you said you turned off Kaspersky and tested but unless you actually restarted the system without Kaspersky loading then all you did was stop the resident realtime scan, all the other elements including the firewall were still in place.
The fact that in Safemode your speed tests are fine is proof that the issue is within your system when all applications are loaded and is not a BT/ISP problem.