Am I having the same problem? Just extended my instrument collection with an Alto Flute and Soprano Choir. At the same time updated my sound sets wit the latest version 1.0.131. Both instruments reject to sound in Sibelius, although they do in Instruments Pro (in Sib. everything double checked, system restart tried, re-installed twice, see screen dump).
Jan Herman Verpoorten
Sibelius 8 (2018.1), Win10 64bit, Intel 8 cores/32GB, VE Pro Server 6.0.16778