I have recently run into the problem of Ksysguard refusing to start. Trying to start it from a console yields an error message:

sysguard: symbol lookup error: /lib64/libQt5WebEngineCore.so.5: undefined symbol: _ZN3re23RE23Arg9parse_intEPKciPv

Running ldd against that library results in the following:

ldd -r /lib64/libQt5WebEngineCore.so.5
undefined symbol: _ZN3re23RE23Arg9parse_intEPKciPv (/lib64/libQt5WebEngineCore.so.5)
undefined symbol: _ZN3re23RE23Arg12parse_stringEPKciPv (/lib64/libQt5WebEngineCore.so.5)

Has anyone else encoutered this and if so, is there a solution?