The second bug is known by Adobe and they are working on a fix. There is a bug fix update coming soon, but I don't know if this is one of the bugs they're fixing.
The first one might be harder to nail down. I haven't seen that issue myself. What format and codec is the footage you're using?
about the frames dropping, I'm working with 4K h264 footage.
What is the source of these 4k files?
You could try the update that came out last night: After Effects CC (November 2017) Bug-Fix Update Is Now Available
It doesn't fix the second issue you mentioned (although, that one is on the list of Known issues in After Effects CC 2017).
This update is 14.0.1 and it fixes several other disturbing issues - especially for Mac users. It does not fix all the bugs that are new with the CC 2017 release but it does fix some issues that have been plaguing After Effects since the first parts of the new architecture showed up in the CC 2015 release. And it may solve your first problem.
If you can't see the update yet, you may need to wait a while until you see it as it can take up to 24 hours to populate an update across all the data centers. You may need to log out, relaunch the Creative Cloud app, and log in again.