@jetdv It is

If they are a partial frame, then you have Quantize to frame issue. Are you sure the project frame rate matches your sources? How do you add the events to your timeline (drag, insert using trimmer, etc)? Also, toggle the Quantize to Frame selection just in case. It should always be enabled.
Edit: Looking again at your pic it is definitely a quantize to frame issue. You should not see the dotted frameline running down on frame 2.

If the left clip did not end on a frame boundary, you must shorten it to remove the partial frame so that it does end on a frame boundary. Then you need to move the right clip left one frame to cover the black hole.

Alternately, just move the clip on the right to the left one frame and it will "slightly overlap" but you'll never notice that.

@Dimitrios, you'd better set your preferences (the internal one) in this way, then see the warning immediately:

@Former user I think I may just have to remake my templates and have the video files on the timeline first to make sure the timeline is set for those files.

Yellandkeil has good advice, That warning has saved me some headaches.

To test if its a frame boundary issue, open Internal Preferences and Show only.... "quantize". Set the two results, "Show unquantized event start and end" to True.

If not quantized, you will see a red bar and the beginning or end of the event. Here's an example, from some iPhone11 HEVC 60P footage showing that the end of the event does not fall on a frame boundary.

I have set the loop to indicate the start and end of the frame. Setting Vegas to Quantize to Frames does not solve this problem for variable frame rate footage.

To actually change the event length to correspond to an actual frame boundary, there's a HappyOtterScripts Free Tool, Quantize to Frames, that will do this. Here's a screengrab of the UI.

After running the tool, the timeline looks like this with the end of the event falling precisely on the frame boundary and you will note that the red bar disappears.

Here's a direct link to the free tool library. https://tools4vegas.com/library/

How does this happen if you started with a 23.976 timeline and only worked with 23.976 footage the whole time? (That's what happened to me).

I changed the internal preferences to show, and this is what my timeline looks like...

This was a 4K timeline at 23.976 with only 4K / 23.976 footage on it. Quantize to Frames is on (I don't even have the toggle button visible, so "accidentally clicking at at some point" isn't an option - as soon as I realized what that button did (about 11 years ago), it's been invisible since.

How does this happen ... ?

A very good question if everything on the timeline is the same frame rate and 'quantize' is enabled. All my video is 25fps yet the red edge warning appears from time to time. I've even had cases where everything is perfectly quantized but when changing the length of an event using Ripple, the entire remainder of the project goes red.

@wwaag Where is the Quantize to Frames script in the paid version? I'm not seeing it.

@Jessariah67

Re the Vegas Pro internal settings, I posted this comment on a very recent post about much the same subject (re Vegas Pro 17 or earlier - in Vegas Pro 18 access to Internal Preferences is SHIFT-Options):

Go to Options and then SHIFT-Preferences. You'll see that there is another tab available named Internal. Go to the Internal tab and in the search field at the bottom of the Internal window type in 'quantize'. There should be only 2 fields showing: 'Show Unquantized event start' and 'Show Unquantized event end'. Change their values from False to True then hit Apply and OK. You might have to then close and restart Vegas Pro (I can't remember if this is needed).

What then happens on the timeline is that any video or audio event that is not quantized will show with its left and/or right edge highlighted in red. You'll then need to zoom in on the timeline very closely so that you can move the frame edge on to the exact frame line at which point the red highlighting will disappear. You'll also need to adjust the adjacent frame so that it abuts firmly up to the same frame line.

Hi Dex. I was able to do that - never realized that option existed - and I'm gonna leave it "TRUE" from now on...

I was actually asking about the Happy Otter Quantize to Frames script - I own the paid version and can't seem to find that particular script.

I think it's not part of HOS but it's a separate free extension wwaag offers here.

@Jessariah67 It is hard to tell from your screen shot, but do the off frame errors appear at the beginning and ending of clips, or primarily one or the other?

@Former user Beginning and ending, because they are on two tracks.

@Marco. Thanks, I'll check that out (weird that "free" stuff wouldn't be part of the paid set, though...

Thanks!

You guys I'd point out that take the proper Ruler in the projectsettings is also very important.

I myself always set it as "Time and Frames" which guarantees no conflict between Video systems (PAL and NTSC). -

@Jessariah67

"Where is the Quantize to Frames script in the paid version? I'm not seeing it."

As @Marco. pointed out, it's not part of the paid version. It's freely available to anyone. The free tools library is really a mish-mash of stuff that has limited application. These tools are very specific to an individual task. Plus, there's just too many of them with more coming.