As the title says, PD17 can't handle lossless videos with the .flv file extension. When you drag them into the timeline, everything seems fine until you do anything. Any action that modifies the video or allows you to view information about the video causes PD17 to hang and stop responding. This happens to any lossless video with the .flv file extension. I have OBS set up to record using the .flv file extension so that the file doesn't get corrupted and unrecoverable if the target application crashes unexpectedly.
There's an annoying workaround to this - put the unedited clip into the timeline, produce it so it becomes MP4, then edit the MP4 instead. Even if it's the same exact bitrate, PD17 can magically handle the MP4 even though only the file extension changed. However, this prevents it from being lossless, ruining the whole point.