If anybody's interested, here's how I solved the issue.
First of all, just changing the ResearchStack implementation version in the build.gradle file from 1.1.1 to 1.1.2 doesn't actually work. I worked around it by implementing a snapshot of the master branch from RS git repo through
jitpack.io.
RS Version 1.1.2 uses sqlcipher 3.5.4, which supposedly supports x64. However, my built APK file still didn't include the x64-specific folders. No luck
So I don't really know why but upping the sqlcipher version to 4.0.0 works just fine. I forked the RS repo and changed the one line of code. Its available at m-szczerba/ResearchStack if y'all want it
Cheers