If you used a script and it worked first time, and you haven’t already checked that the script didn’t toggle itself off, I’d start with that. Always had that thing happen to me with a custom script I added to VLC and had to remember to toggle it each time I started VLC

I’m not super familiar with VLC but I asked a chatbot, does this help at all?

1. Open your video with VLC.
2. Navigate to the scene that you want to capture. You can use VLC’s frame-by-frame feature to access a specific frame in your video.
3. Capture the screenshot by pressing Shift+S (Windows and Linux) or Command+Alt+S (Mac).
4. Alternatively, from VLC’s menu bar, select Video > Take Snapshot.

If you’d like to use advanced controls to capture the screenshot, then from VLC’s menu bar, select View > Advanced Controls to enable those controls. Then, in VLC’s bottom-left corner, click the camera icon to take a snapshot1.

Your screenshot is now captured and saved in a folder on your computer. The default location for the screenshots is as follows:

1. Windows: C:\\Users\\username\\Pictures
2. Mac: Desktop/
3. Linux: ~/Pictures

If you’d like to change where VLC stores your screenshots, or you’d like to change the file format, then select Tools > Preferences from VLC’s menu bar. On the “Simple Preferences” window that opens, select the “Video” tab. To change the default screenshot directory, then in the “Video Snapshots” section, click “Browse” next to “Directory.” Then, choose the new folder that you want to set as the default for your screenshots. If you’d like to use a different image format (the default is PNG) for your snapshots, then click the “Format” drop-down menu and choose a new format. Your options include PNG, JPG, and TIFF. After you’ve made the changes, at the bottom of the “Simple Preferences” window, click “Save” to save your changes.

Can you post a screenshot for the location for them save in your Settings?