Some plug-ins that have been installed before are fine if placed under the bundle and run without problems.
Today I installed a webapi-vim plug-in. According to the README, it supports bundles. Looking at the GitHub issue, some people have successfully installed it. But after cloning to the bundle, an error is reported.

Error detected while processing /Users/mc-zone/.vimrc:
line   47:
E117: Unknown function: webapi#json#decode
E15: Invalid expression: webapi#json#decode(join(readfile(expand('~/.snippets.json')), "\n"))

is because I have a statement in .vimrc that uses its function. It is used to configure the extension abbreviation snippets.json for emmet-vim. (These two plug-ins are by the same author, emmet is under bundle).

But when I copy the files under the webapi plug-in such as autoload to the corresponding .vim/autoload, it can be used.

There have been cases before where the plug-in installation did not support pathogen. bufexplorer.vim, grep.vim These two must be installed under .vim/plugin/.

Is there any good debugging method to know what the problem is? Or check the pathogen running/loading status?