Found that using AVCHD format in V13 makes playback laggy (around maybe 10FPS) and really slows workflow down. The slowdown only showed up on 13.1, didn't occur in 12 or older. I'd do transcoding but I have too much footage and transcoding would take way too much time. Computer specs as follows:
CPU: Intel i7 7700HQ
RAM: 16GB DDR4
Graphics Card: NVIDIA GTX 1050 Ti Max-Q 2GB VRAM
Drive: 512GB PCIe SSD
Hope they'd address this issue on the next update.