I have a similar issue.   If I'm reading the backtrace correctly, this appears to be an issue with libQt5Core.so.5.15.2. 

I'm trying to run kstars-bleeding 3.5.4+202107081131~ubuntu21.04.1 on two machines recently upgraded to 21.04 with same result.

I have attached a backtrace for reference and have also raised a bug on bugs.kde.org.

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File Name: gdb_bt_kstars_2020-08-08.txt
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