By USB Storage you're talking about connecting something like a USB flash drive or SD card reader to your phone using a special cable, correct? I've been meaning to buy one of those adapter cables, but haven't got around to it. (If I get around to getting one in the next few days I'll let you know if I have the same problem with my ART configured m8.
Verizon's website says the m8 doesn't support USB storage, but you're saying you had it working on your m8 using Dalvik, correct? (Where you using 4.4.2 or 4.4.3 with Dalvik, and how about with ART - are you using the same version of the OS)?
USB Mass Storage - The all new HTC One® (M8)
HTC's website has it listed as a type of storage in their m8 section, so I wouldn't be surprised if Verizon's website has incorrect information.
HTC One (M8) Support - Types of storage | HTC United States