On the latest version of Kleopatra I've been experiencing the below error on a key search:
"Failed to search on certificate server. The error returned was: Syntax error in URI"
Oddly results are still returned from the search and there appears to be no issue with those results.
I have a user that reported this issue, and I could not reproduce while on an older version of Kleopatra but as soon as I upgraded to 4.0.2 I also began hitting the error.
If it matters we have our key servers set to hkps://keys.openpgp.org but no other configuration changes.
Please let me know if further logging/information is needed.