Please share a clip that has the issue, to see if a necessity to 'reprocess' can be replicated.
Be sure to allow the green caching line above the tracks to complete or PV may not be smooth. If this is a multi-track project wait also for the line under the PV window to change color - purple or gray. That confirms that the sequence is cached.
Clear the disk cache prior to beginning a new project. It can also be cleared at anytime during editing.
To select all clips on a track, select the first. Hold down <shift> and select the last. Press DEL on the keyboard. That's a standard Windows thing.
To apply effects to multiple clips, select the clips, right-click on one
icon to program the effect, then click the "replace effect chain" button on the effects toolbar... 
Be sure to file your other suggestions with the company... https://www.nch.com.au/suggestions/index.html
Also, for HD, lengthy or complex projects use the 64-bit releases.that take better advantage of PC memory.