To animate a sequence of images efficiently in Spine, you can utilize the "Sequence" feature introduced in Spine 4.1. This feature allows you to set up an attachment to have a sequence of images, which you can then control the playback of by keying the sequence. This eliminates the need to manually make each frame visible and invisible, significantly speeding up the process.

For the issue with the small red cross and the missing image icon, it indicates that Spine cannot find the specified image file for that frame. This could be due to a naming issue or because the image file is indeed missing from the expected directory. Ensure that all your image files are correctly named and located in the directory Spine is looking in. If your images have leading zeros in their numbering (e.g., 01 instead of 1), make sure to specify the start/end numbers with leading zeros in the sequence setup.

For detailed guidance on setting up and using sequences in Spine, you can refer to the official documentation and tutorials provided by Esoteric Software. Additionally, checking the naming convention and file paths of your images can help resolve the issue with missing images.

If you could see the image before checking sequence, make sure that you formatted the name correctly in the path field as in the gif below:

Likely a piece is missing from either the sequence number or the path.
If you're still having problems please post the full name and a screenshot of how you set it in the Sequence properties.