I do not want to offend anyone but is the concept regarding linking real time (SMPTE) and musical time (bars and beats) really so hard to grasp?
Say, you have a song at 120 bpm in 4/4 and a marker at SMPTE 1:00 which is beat 1 of bar 31. The marker is attached to the SMPTE Time and will show you where in the score that point is.
The marker is NOT attached to bar 31!!!
When you change the initial tempo to 240 bpm you will have twice as many bars in the same time, hence the marker, which is STILL attached to SMPTE time 1:00 will now be displayed at bar 61, because beat 1 of this bar is now at this time position.
The marker does NOT change its time position, but it will MOVE in the score to show you that now another bar falls onto that position.
If you have composed music that started at that original position you must understand that your music did not start on SMPTE 1:00 but in bar 31 which at a tempo of 120 bbm happens to coincide.
After changing the tempo the music still starts in bar 31 which now does not anymore coincide with SMPTE 1:00, hence the marker will be shown at whatever bar is now falling onto SMPTE 1:00.
Also a less drastic tempo change like a ritardando shortly before bar 31 will have the same effect. Dorico interprets the “rit.” text and performs a slowing down of the tempo which means that at SMPTE 1:00 your music will not have arrived at bar 31, therefore the marker will (still not move, it stays firmly connected to SMPTE 1:00, but) be displayed a little earlier in the score to show you what beat now coincides with SMPTE 1:00
This is the intended and logical behaviour!
What you want is some kind of 2nd level attachment: you want a new musical section (or cue) to start at a specific SMPTE time regardless of what is happening before.
As a long time logic user myself I would also very much hope for such a solution which could be called a “Cue marker” (in contrast to SMPTE marker):
If I would rise the tempo before such a cue marker the programm would insert bars to fill the time up to the fixed cue marker and probably one incomplete bar or another tempo change only for the last bar (to make it into a kind of fermata), or the other way round: if I lower the tempo before such a cue marker the music before that marker would “disappear” (but stay in memory, imagine overlapping regions where only the region that starts latest will be played).
Dorico offers you exactly this kind of solution by starting a new flow at every new cue as has been suggested here for multiple times.