Unable to download jEdit plugins on openSUSE Leap 15.2

I am using jEdit 5.1.0 (and openjdk 11.0.8 2020-07-14) on openSUSE Leap 15.2 and unable to install plugins through its plugin manager. Each time I select a plugin and click the Install button, the plugin manager gives me the following error message:

I have tried both the Plugin Central default (on SourceForge) and several mirrors (e.g. NetCologne GmbH, DEAC (Frankfurt am Main), Free France (Paris) and Vorboss (London)), but each time I get the same error.

Temporarily turning off the firewall (sudo systemctl stop firewalld) does not help.
Trying some of the same download mirrors on my MX Linux machine (jEdit 5.5 and openjdk 1.8.0_272) does not lead to errors, so it seems that the issue is specific to openSUSE (or the jEdit version I am using?) and not because of issues with the download mirrors.

How can I solve this issue?