My suspend did not correctly since I installed a USB 3 extension card in my PC. Instead of going to S3, the computer just woke up instantly. dmesg gave the hint "usb_dev_suspend+0x0/0x20 returns -2" so I rmmod'ed the "xhci_hcd" module which did the trick.
Is there a good way for me to work around this? The builds from the Kernel Mainline PPA did not help, unfortunately, and blacklisting the module is not my favorite option. Where is the best place for me to report this issue?