Hi Linc,
After reinstalling Flash, the issue came back again. I didn't experience it though until I opened Youtube which most likely used Flash. I managed to capture it on video which can be viewed HERE. As you may notice on the video, I was clicking the whole time and nothing is responding. No spinwheel. Just pure freeze and then after a few seconds, UI just scrambles back to normal. Now it's acting up on random even though I've already closed the tab. I also got this log list from Console when a freeze occurred just as you suggested. I marked some lines which I can conclude to be irrelevant to this issue though correct me if I'm wrong. I'm thinking the only solution I have here is to remove Flash and wait for some update regarding this issue.
08/10/2015 9:27:03.078 PM sharingd[468]: 21:27:03.078 : BTLE scanning started
08/10/2015 9:27:03.079 PM sharingd[468]: 21:27:03.078 : Scanning mode Everyone
08/10/2015 9:27:03.079 PM sharingd[468]: 21:27:03.079 : BTLE scanner Powered On
08/10/2015 9:27:03.118 PM sharingd[468]: 21:27:03.117 : BTLE discovered device with hash <018f5599 4b230f00 0000>
08/10/2015 9:27:03.118 PM sharingd[468]: 21:27:03.118 : BTLE scanning stopped
08/10/2015 9:27:18.121 PM sharingd[468]: 21:27:18.120 : BTLE scanning started
08/10/2015 9:27:18.121 PM sharingd[468]: 21:27:18.121 : Scanning mode Everyone
08/10/2015 9:27:18.122 PM sharingd[468]: 21:27:18.121 : BTLE scanner Powered On
08/10/2015 9:27:18.147 PM sharingd[468]: 21:27:18.146 : BTLE discovered device with hash <018f5599 4b230f00 0000>
08/10/2015 9:27:18.147 PM sharingd[468]: 21:27:18.146 : BTLE scanning stopped
08/10/2015 9:27:21.343 PM sharingd[468]: 21:27:21.342 : Bonjour discovery stopped
08/10/2015 9:27:21.344 PM sharingd[468]: 21:27:21.343 : BTLE advertising stopped
08/10/2015 9:27:21.345 PM sharingd[468]: 21:27:21.344 : Finder exited AirDrop
08/10/2015 9:27:21.345 PM sharingd[468]: 21:27:21.345 : AirDrop server disabled
08/10/2015 9:27:21.345 PM sharingd[468]: 21:27:21.345 : BTLE scanning started
08/10/2015 9:27:21.345 PM sharingd[468]: 21:27:21.345 : Scanning mode Everyone
08/10/2015 9:27:21.346 PM sharingd[468]: 21:27:21.346 : AirDrop server terminated
08/10/2015 9:27:21.346 PM sharingd[468]: 21:27:21.346 : Bonjour advertise stopped
08/10/2015 9:27:21.347 PM sharingd[468]: 21:27:21.346 : BTLE scanner Powered On
08/10/2015 9:27:21.755 PM sharingd[468]: 21:27:21.754 : Terminate AirDrop P2P link
08/10/2015 9:27:35.997 PM WindowServer[377]: disable_update_timeout: UI updates were forcibly disabled by application "Console" for over 1.00 seconds. Server has re-enabled them.
08/10/2015 9:27:36.010 PM WindowServer[377]: common_reenable_update: UI updates were finally reenabled by application "Console" after 1.04 seconds [0.96fps] (server forcibly re-enabled them after 1.03 seconds [1.00fps])
08/10/2015 9:27:51.000 PM kernel[0]: IO80211AWDLPeerManager::monitorAWDLState Disabling AWDL due to no services and no active sockets
08/10/2015 9:27:51.000 PM kernel[0]: ARPT: 11710.064067: AWDL Sync Enabled 0, data path state[1]