[Qgis-user] Inconsistent label positioning

[Tom Christian]

I'd like to know if there's anything I can change (e.g. a well-buried
advanced setting or environment variable) to remove pseudo-randomness
within QGIS's label positioning.

I have a QGIS project version-controlled within Git and a process to export
layout PNGs from the base (before) commit and the head (after) commit when
a change is made. These images are compared and any variation flagged to a
reviewer so that they can verify each change is intended and expected
before merging to the main (release) branch.

I have line label positioning configured as "Preferred Placement Hint"
rather than "Strict" positioning as the result is significantly better when
I allow QGIS to make placement decisions on my behalf. However, in this
configuration there is some pseudo-randomness where QGIS sometimes makes
minor changes to label positions even though neither the data, the layout,
nor the export configuration have changed. This leads to false-positives
during change analysis.

Here is a GIF showing 5 sequential exports in which two line labels move
slightly. Each of the 5 frames shows for 0.5 seconds:
https://www.dropbox.com/s/x3y4vfr20s9inqw/print-map-label-movements.gif?dl=0.
One change is at "West Connector" near the centre of the image and the
other is at "The Dip" near the centre of the inset map.

I previously posted this question on gis.stackexchange but so far no
traction, so any input would be very much appreciated (
https://gis.stackexchange.com/questions/416430/qgis-inconsistent-label-positions-in-png-pdf-layout-exports
).

Thanks
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