For uploaded videos Spotlightr creates multiple resolutions as you may know.
These resolutions serve to serve the optimal video quality in comparison to the viewer's connection speed.
However in some use cases, such as with text heavy videos, where you are for example recording your screen and have small print data points or copy which needs to be legible, loading a lower quality resolution will not suffice.
This is why you have the option to always force the highest resolution on your videos if this is important to you. To do so, go to your Spotlightr Application Settings and check the option "Disable Resolution Auto-switch"
With this option turned on the highest available resolution will always load first and it will never be switched on it's own regardless if a drop in connection speed is detected. The only way a resolution can be switched is if the viewer requests a lower resolution via the player options settings menu.