Q: MacBook syncs with LG monitor with low frequency after Standby

Dear community,

I'm using a MacBook Pro 13" Early 2015 together with LG 34UC87 display with native resolution of 3440x1440. The device is connected using the Apple Thunderbolt cable. Everything is fine if I freshly connect the screen to the MacBook in clamshell mode: Syncs with 50 Hz. But after leaving the MacBook alone in this setting and waking it from standby later, the screen only syncs with 30 Hz. System preferences doesn't allow changing the frequency - the combo box is greyed out. If I then unplug the cable and connect it again, the issue is solved: Again, 50 Hz. But that's not convenient as this removes the Firewire drives I have connected to the Thunderbolt hub of the screen.

I already tried resetting System Management Unit and the PRAM. Any other ideas?

Best regards

Chris