EXPO is AMD's extended profile for overclocking. When you enable it, the memory runs at the manufacturer rated speed and timings. When you disable it, the memory runs at SPD default speed and timings.
https://www.amd.com/en/products/processors/technologies/expo.html
The GPU speed is likely spiking because there is a process running that is occasionally using it, such as video ads in a browser window for example.
Ryzen R7 5700X | B550 Gaming X | 2x16GB G.Skill 3600 | Radeon RX 7900XT
Ryzen R7 5700G | B550 Gaming X | 2x8GB G.Skill 4000 | Radeon Vega 8 IGP
Ryzen R5 5600 | B550 Gaming Edge | 4x8GB G.Skill 3600 | Radeon RX 6800XT