I have a Black Widow Chrome 2016. I got the PBT keycaps. I had issues with the Spacebar, Enter, and Backspace sticking when pressed. Razer support was no help and I wasn't able to find anyone else reporting the issue. I discovered that the keyboard stabilizers and the keycap stabilizers are not universal. The Keyboard stabilizers on my Widow were much thicker bigger than the ones newer keyboards use. The included key stabilizers do not fit on the board stabilizer that was already on my keyboard and caused issues and jams. I replaced the board stabilizers with a set of Max Keyboard mounted stabilizers and the caps work perfectly.

Gallery outlining differences: https://imgur.com/a/j5Io02Z

Replacement Board stabilizers: https://www.maxkeyboard.com/cherry-mx-plate-mounted-stabilizer-clips-4-pcs.html

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TL;DR: If you get the PBT keycaps, you might need to replace the board stabilizers on your keyboard.