GNU GLOBAL (gtags) is not available for Go source files

I ran gtags in the directory where the source code for Go resides and generated a tag file.

After creating the tag file, I tried to jump the tag using gtags.vim (vim plug-in included with GNU GLOBAL) in vim, but it became Not Found and I couldn't jump well.
Why?

The generation of the tag file seems to have been successful without any errors.

I also tried the global-xr command, but nothing was displayed.

By the way, gtags do not support Go by default, so we use pygments to analyze them.

Environment:
Arch Linux GNU GLOBAL 6.6.5