What is your operating system?
What is your Shotcut version (see Help > About Shotcut)? Is it 32-bit?
Can you repeat the problem? If so, what are the steps?
(Please be specific and use the names as seen in Shotcut, preferably English. Include a screenshot or screen recording if you can. Also, you can attach logs from either View > Application Log or right-click a job and choose View Log.)
Add 3 ranged markers on the timeline
Delete the first one added
Save, exit, reload project
Create a new ranged marker
Try to export one of the ranges. The output will not be of the expected marker range but one of the other ranges (consistently, I assume the indexes in the export list aren’t updated with the real ones after the deletion).
Here’s a short .mlt that has the bug, used the open other->color so no videos needed.
markers test.mlt (5.2 KB)