Some troubleshooting advice from someone who works in tech support:
Keystrokes are sent to software applications by the operating system. Media keys are standardized, so the data that is sent is always the same. The issue in most cases like this is that the data is being sent somewhere other than where you expect it to be sent. Check your running processes, is there another media player running in the background?
Software to manage keyboards can also trip things up. If removing that software corrects the issue, you should be on a forum for that software asking for support or, better yet, contacting the software developer's sort team directly.
Home Desk ~ MB 3.3 Portable • Questyle CMA400i (ASIO) • Sennheiser HD 660S (balanced) / Audeze EL-8 Closed Back / Fostex TR-X00 Ebony • Teac AI-101DA • Jamo C93 + Dayton Audio SUB-1000
Work Desk ~ MB 3.3 Portable / Tidal • SMSL SU-8 v2 • Nobsound NS-05P • THX AAA 789 • Sennheiser HD 58X (balanced)
OTG ~ FiiO M11 • Audiofly AF180 / B&O H6