Last night I fired up KStars 3.5.3 on Win10 for the first time in ages and searched for and found Comet Leonard without doing anything special. Today I upgraded to 3.5.6 and Leonard is nowhere to be found. Tried updating Comet Orbital Elements but still no Leonard.
When I installed 3.5.6 the comets.dat under App Data\Local\kstars was still dated 31/5/2021. Some files had been shifted across to App Data\Roaming\kstars but comets.dat was not one of them
I uninstalled 3.5.6 then re-installed 3.5.3 and Leonard reappeared.
Added:
Also tried copying comets.dat to Roaming\kstars under 3.5.6 but still no Leonard