Error message temporarily appears when reloading Dashboard settings pages

Description of problem:

When reloading `Settings > Notebook images` and `Settings > Cluster settings` page in the Dashboard, a temporary error message appears and it disappears very quickly. It doesn't happen with other pages in the dashboard.

The error message is:

You find a GIF attached to this issue showing the process.

Prerequisites (if any, like setup, operators/versions):

RHODS installed (reproduced on v1.15.0-10, but it may be present in older versions too)

Steps to Reproduce

1. log in RHODS Dashboard with a rhods admin user
2. go to Settings > Notebook images`
3. reload the page and notice the error message
4. go to `Settings > Cluster settings` page
5. reload the page and notice the error message

Actual results:

error message temporarily appears in the web page

Expected results:

no error message appear after reloading the web page 

Reproducibility (Always/Intermittent/Only Once):

Always (reproduced on v1.15.0-10, but it may be present in older versions too)

Build Details:

v1.15.0-10

Workaround:

Additional info: