Package: libmuscle1 Version: 3.7+4565-4 Severity: grave libmuscle-3.7-1 in stretch ships libMUSCLE-3.7.so.1 libmuscle1 in unstable ships libMUSCLE.so.1
It is not clear to me whether or not this library name change was intended, but providing libmuscle-3.7-1 in libmuscle1 is currently wrong and the root cause of bugs like #904690.