RX 580 memory overclocking

[TGS96]

Hi everyone!
Let me share something I have been noticing for the last 3-4 hours: I was stubbornly (?) trying to beat #1 Time Spy for i5-2400 + RX 580 systems. I was obviously going to try by overclocking the sh*t out of my GPU. Well, after like 30 runs of Time Spy I gave up due to thermal throttling (it was pointless to try this today since it's a sunny 36 °C day) and poor memory overclocking: even with 1200 mV on the memory controller I only managed to get to 2025 MHz and it wasn't even fully stable (memory voltage was set in WattMan); keep in mind that I was achieving 1480 MHz with a core offset of +40 mV. So I went to Afterburner to wipe my overclock and reapply my original settings: -200 mV and 1300 MHz on the core. Then I tried, just for the sake of it, to overclock my VRAM again: now it sits stable at 2250 MHz at stock voltage (950 mV).

So my question is: how GPU overclocking can have an impact on VRAM overclocking? Was it a thermal issue, was it due to VRM design or something else? Have you ever experienced something similar?