Using Sibelius 7, VDL 2.5, Kontakt player 5. Whenever I write a tremolo (I'm using the three slash option from the keypad tool), the sound gets extremely soft. For example, in my timpani part, single hits play back loudly, at whatever dynamic I set, but then a roll always plays back extremely quietly. I don't have any sort of template in place, but I haven't had this problem in the past, it seems to be recent since I reinstalled VDL on this computer to use with Sibelius. Any suggestions? Thanks!

By any chance are you using an older library version? Here's an article that tells you how to tell which library you're using:
https://www.tapspace.com/support/faq/index.php?action=artikel&cat=4&id=127&artlang=en

If you're not using library 2.5.5, that might be the problem. There were some issues in older versions of the library that caused certain sounds to perform very quietly due to expression defaults. It sounds like that's what's happening in your situation. I'd recommend updating to 2.5.5 if you haven't already.

You can learn more about the 2.5.5 library here:
https://www.tapspace.com/software/2.5.5-library-update-for-vdl/