Short Version - a suggestion.
Try Download macOS High Sierra 10.13.3 Combo Update
The "Combo" includes the full version of High Sierra 10.13 along with its latest .3 update.
(It will NOT erase your data. It can be used to install a macOS X on a formatted HD.)
Long Version - my fun.
After a very long struggle, Siri works and I haven't seen any system-wide "hiccups". I think the video freezes made it more obvious.
A month ago, thinking it might speed things up, my internal HD was formatted for APFS using Command-R. That went rather quickly, just a few minutes. I can't say for sure if APFS started the "hiccups/freezing".
I tried the Time Machine drive, after 3 HOURS, it said it was unable to format that drive as APFS.
I wanted to reinstall the OS High Sierra, hoping it would fix the problem, but Command-R could only install Yosemite. Huh? Ummm, I don't think so. Disappointment and sadness Apple couldn't modernize Command-R by now.
I opened Command-R's Disk Utility to see if it needs repair. It didn't show. It must really be damaged. But Time Machine showed. It must be the OS X HD. Further disappointment, you can format for APFS but Apple can't see APFS if you need any help.
The quickest solution is to by a new external HD. Did a quick look around, both, Amazon and Best Buy had an external USB3 2Tb for $69 (internal was just 1Tb). Being there's a Best Buy just 1 mile away, it was a no-brainer.
Before attaching it, I wanted to see if the High Sierra's Disk Utility is better. Not only did it see the drive, but it fixes several errors it found. Should I have done this first? Was the new drive needed? I don't think I would have considered to wipe the drive and download the combo. It found errors, but it was still not working properly. It was an endless cycle.
Knowing there is no way I was going to allow Time Machine to install the OS on the new boot drive, I did a format to HFS, then the combo install, Download macOS High Sierra 10.13.3 Combo Update. It went as expected, about an hour. Siri worked perfect.
But, after that happiness, there was terror. I saw no other way to move all of my data (passwords, settings, etc.) other than going back to Command-R and selecting "Restore from Time Machine Backup", hoping the new OS install won't be written over. That took about an hour, too.
As it was doing that, I left to shop a little and get a bite to eat. I wasn't too confident I'd see my desktop with a working SIRI again.
It worked! I must have asked it a dozen stupid questions. It wasn't perfect, I did see a couple of those "SiriNCService quit unexpectedly" errors, but it keeps working. I was stopped by the "com.apple.asistant" requesting my Keychain password. From over 5 years ago, is it serious? Nothing I knew worked. Siri locked me out.
I have no idea why, but in the Keychain Access menu Edit > "Change Settings for Keychain Login..." it accepted my account password, when nothing else would. Being that I liked it, it accepted that as "old" and the same thing as the "new". "Always accept", Siri was back.
I haven't seen any freezing/"Hiccups" in the past few days.
I'm saving APFS for another day. When Command-R supports their own file system and current OS (they can easily see if my machine is compatible with a particular version, check it for updates), I may reconsider.
As they have said hundreds of times in the past, good advice was always "Try the Combo Update". MS Windows has "power off, then power on, call us tomorrow if you have problems", macOS X has "install Combo Update".