Windows does not allow other windows to draw on top of a game running in exclusive fullscreen — the same mechanism that makes your screen flash when you Alt-Tab out of a fullscreen game. This blocks the Companion App overlay and can also break Overwolf overlays.
Fix: switch to borderless fullscreen
- Open the game's graphics/display settings.
- Change Display Mode from Fullscreen to Borderless (also called Windowed Fullscreen).
The game still fills the whole screen at your monitor's resolution — on most setups there is no visible difference — and the overlay shows immediately.
Prefer to keep exclusive fullscreen?
- 2nd screen mode — show the map on a second monitor.
- Peer Link — use a phone or tablet as a live minimap.
Related: Performance issues.