Failed to open plugin management

[yuyongsong]

Describe the bug
A clear and concise description of what the bug is.

To Reproduce
Steps to reproduce the behavior:

1. Go to '...'
2. Click on '....'
3. Scroll down to '....'
4. See error

Expected behavior
A clear and concise description of what you expected to happen.

Screenshots
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Server (please complete the following information):

• Etherpad version:
• OS: [e.g., Ubuntu 20.04]
• Node.js version (node --version):
• npm version (npm --version):
• Is the server free of plugins:

Desktop (please complete the following information):

• OS: [e.g. iOS]
• Browser [e.g. chrome, safari]
• Version [e.g. 22]

Smartphone (please complete the following information):

• Device: [e.g. iPhone6]
• OS: [e.g. iOS8.1]
• Browser [e.g. stock browser, safari]
• Version [e.g. 22]

Additional context
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[heldersepu]

Hard to troubleshoot when all you provide is an image...

Here is one image:

As far as I can see it works with the latest version