Stutter playback on rendered MP4 files on Apple devices

Few months ago I got negative feedback from one client about the playback quality of the short commercial I made for him. Playback was stuttered (choppy) only on his Mac and iPhone. On his Android phone, he said, playback was smooth.
Yesterday I got the same complaint from another client. The only thing I found helpful in both cases was to render that file again in Adobe Media Encoder with default settings for .mp4

My settings in Resolve in both cases was:

format: MP4
codec: h.264
encoder: NVIDIA
network optimization checked
resolution and frame rate was the same as source file
quality was restricted to 16000-20000 Kb/s (I also tried with lower quality - 5000Kb/s, but that didn't solved the problem)
encoding profile: auto
Key Frames: Automatic
Frame reordering checked
Rate control: VBR High Quality
Lookahead 16 frames
Adaptive B-frame enabled...
All in all almost every setting was on its default.

On any PC (more than 10 of them) I tried, the playback was smooth. On all Android devices (18 of them) I tried to play, everything was OK. Only on 3 Mac devices (those 3 were only Mac devices I could try to playback on) and on 6 different iPhones and one iPad I had the problem. All of them suffered from stuttering (choppy) playback.
But, the moment I rendered a "problematic" file in Adobe Media Encoder with default settings for MP4 (h.264) the problem was solved. On all mentioned Mac, iPhone and iPad devices, now playback was smooth.
Does Anyone have an idea what could possibly be wrong in my render settings (or wherever) in Resolve?
Thanks!

I don't know what the issue, but I'd try with constant quality rate control. Noone uses VBR these days.

I'd try, thank you.
When you choose MP4, VBR is set as default, therefore I didn't try to change it.

VBR per se shouldn't be a problem, but maybe the peak data rate is too high?

I tought that high data flow could be a problem, but it isn't. Even when I limited data rate to 5000Kb/s problem remains the same.

Are you sure it actually adheres to those rates? Can you paste MediaInfo of such a file?

I can't right now, but I'll do it in a few hours.

Are you sure it actually adheres to those rates? Can you paste MediaInfo of such a file?

Here are the Media info for both files.

Adobe Media Encoder vs. DaVinci Resolve.jpg (551.66 KiB) Viewed 987 times

A bit late to this convo, but I've had this EXACT issue. I narrowed it down to the nvidia render option. In my tests, it was only a problem when I used the GPU(nvidia) render. Using CPU, renders played fine on mac devices, with the nvidia render they did not. Granted I didn't drill down into specific nvidia settings, I just rendered with the CPU and moved on.

But I'd love to be able to render with my GPUs as it cuts my renders in half, and to not be afraid clients randomly won't be able to play files. Anybody have any insight on this?