Bug PC Master build lags with lot of spikes, Editor is fine (same resolution)

Hello,

I have a bug with a recently bought graphics card (GTX 1660 Super) that I didn't have on another PC before (which has a GTX 1050 Ti).
Our project is a PC UWP game which uses Windows Holographic Remoting to stream content to a Hololens 2 headset.
I don't know exactly how this works, but either in the editor or in the player build, the game is supposed to render two video frames per frame, one for each eye, at the resolution of 1268 x 720.
Although the player build runs fullscreen at 1920x1080, I think the content is derived from one of the eye render targets.
And I didn't have this problem on a previous PC (less powerful) with a GTX 1050 Ti.

Here's the output of the profiler for the two tests I did (the player build on the left, editor on the right):

Player Build timeline selected:


Editor timeline selected:


As you can see, the player build seems very spiky whereas the editor is very stable.
The lag is from the spikes going above the 60 FPS limit, because the HoloLens always needs 60 FPS for a stable experience, not less.
If someone is interested in the profiling data, here's the link to the .data binary: https://we.tl/t-9TniI5nXal

It seems that Camera.Render takes ~0.33 ms in Editor and 5-10 ms in Player build, so rendering may be the issue.
With this project the graphics settings I can edit are in the Quality tab of Project Settings, and also in the MixedRealityToolkit asset (Camera -> Display Settings -> both Opaque and Transparent let me choose a quality setting). I don't know which one controls the other, or even what is used in the Editor/Player build.
Those three quality settings are set to Medium. The Player build of the same project worked well on the other PC.

The other PC had Windows 10.0.18362.0 installed, and this one has 10.0.19041.0.
I use the Windows Mixed Reality 4.2.1 package, I don't use the new XR plugin management.

Sorry to bother you if it's some little thing I forgot to do, but in case someone knows what is going on... Any help is appreciated!
Thanks!