First is the most obvious bug, although I have asked around and not everyone encountered is experiencing this issue. The Emote Wheel (haven't checked the Quick version, only the normal one) has overlapping textures of itself with empty slots. The actual interface functions normally. This issue also affects the Ping "wheel" as well.
This was tested on the PBE 7/7/2019 at 3:10 PM on Windows 10, 1920x1080 screen resolution. The bug is persistent and consistent across all game modes.
Second is one you probably already know about, and is also not exclusive to PBE (it's a bug on live as well.) Yasuo's Windwall. Non-skillshot projectiles (and many skillshot projectiles which are not controlled mid-flight) will not interact with the Windwall until the windwall's "deploying" animation is finished. More often than not, it can be tested with auto-attacks right before they hit yasuo. If this change is intentional, it sure doesn't seem like it. The active frames of the windwall upon cast are likely delayed or misplaced/displaced somehow. For the champion itself, this can be game-breaking, especially for a practiced player who is used to being able to rely on last-second windwalls.
Not entirely a bug, but the Demacia Vice skins and chromas were not given the 1 BE treatment that was common for new skins. If this was intentional, I don't entirely agree, but I understand and don't mind much.