EASY steps to re-create the issue:
1) Enable GPU Accleration in your Project Settings.
2) Create TWO sequences and add a bunch of clips to your timeline in EACH sequence.
3) Apply an effect like "Warp Stabilizer" to all those clips (or, if you have like 30 short clips add it to say half of them) on each of the two sequences.
4) Wait for the effect to finish working/stabilizing and you'll notice the render bar where the effect was added gradually turns from RED back to YELLOW for smooth playback.
5) You can now toggle back and forth between the two sequences easily and play, edit, etc. All is well at this point...
6) BUT!!!!...once you save the project (or if the project AUTO-SAVES) then now when you toggle back to the other sequence the render bar has returned to RED and you have to WAIT for it to turn YELLOW again which sometimes can take anywhere from a several seconds to 1/2 a minute or even more (depending on how many effects (warp stabilizers in my case) you've added). During this delay, you cannot work or even play the video on BOTH timelines. Once it switches back to YELLOW you can work like normal...until it's saved again.
NOTE#1: If you toggle OFF GPU Acceleration for the project and set it to "Software ONLY" then this issue/delay does NOT occur.
NOTE #2: Another pain is that to save the project above takes upwards of 45 seconds!!!! When I turn off GPU Accleration, saving takes only up to a few seconds. Imagine have to stop work and wait 45 seconds every time your project auto-saves!
This delay above is a real pain when I have multiple sequences with effects and after every time I save the project (or after it's auto-saved) I have to initially sit and wait 30 seconds or more sometimes when I go between sequences.
Why does simply saving a project trigger this issue/delay?
Is this a bug that I should report?
I've tested this on 2 different Mac computers (2011 iMac w/ AMD6970M (1GB VRAM) GPU as well as the supported 2012 Macbook Pro with NVIDIA GeForce GTX 650M GPU w/ 1GB VRAM) with the same results.
Switching between timelines and auto save is a real pain when Warp Stabilizer is applied many times.
No Warp no lagging. So its definitely the Warp Stabilizer effect also on PC.
Well, thanks Ann for testing and confiming the issue on a PC as well.
Bug report submitted.