Basically as it says in the title.
I’m working on the Create With Code project, prototype 5 (see here). At step 4, game objects have a script that send them into the air and fall.
With the same script, they fall smoothly in 2020.2.0a15, they don’t in 2020.2.0a16, they seem to stop every second. This is the best description of the problem I can give.
Please, nobody answers that “you should use the recommended version for that tutorial”, thank you. 
@LeonhardP This problem happens also in a18.
As always, your best bet is to file a bug report with a simple repro project.
If I had to guess, you are using Mac and are seeing some side effect of this a16 change:
“Core: Improved Time.deltaTime consistency for Metal graphics API on iOS and macOS”
I’m on Linux Mint and Mint not being supported, I cannot file a bug report. The problem is not related to Linux since this doesn’t happen in a16.
Have you considered installing a supported distro for testing out alpha versions? I bet that would be more productive that tagging LeaonhardP in almost every post you make
Ubuntu doesn’t run on my computer. That said you are right, I’d better no longer post anything about things that do not work properly for me. We, who do not use Ubuntu, stink.
Now, it’s very easy to reproduce:
install a16 and a18,
in both create a new empty project,
on the scene place three objects: a cube, a sphere, a cylinder, at y = 10,
add to each of them a rigidbody,
press Play and compare how they fall in a16 and a18.
Any Mac or Windows user can do that too, just to see if it happens to them, not forgetting CentOS and Ubuntu users.
This is my last post on that matter.
This problem is related to that one: Awful Editor Game Start Time
After building the project, the objects fall smoothly.
Problem related to this bug: Unity Issue Tracker - Linux Editor has low performace in Playmode on a new project
Thread can be locked.