ASM cookie without value not RFC-compliant

I'm seeing the same issue after upgrading from 11.3.0 to 11.5.1. Before upgrading, one of my ASM profiles generated an abnormally large number of 'ASM modified' violations. After the upgrade, the same profile generates an abnormally large number of 'Cookie not RFC-complaint' violations instead of the 'ASM modified' violations. Viewing the violation details lists the cookies that have been flagged are all TS cookies which have not value (TSxxxxxxxx=;) Does anyone know what the root cause for this behavior?