I have recently problems with the legend. In one situation, I changed the symbology labels manually. The changes showed there, but only partly in the TOC and the legend. So as a solution, I changed the text directly in the TOC. Sometimes I also have problems, that the legend changes in the exported version (differently in different attempts). What are the possible reasons? could it be connected to special characters from languages or the "<", ">"? Or could a re-installation of ArcGIS Pro help?
In the screenshot the bottom is the ArcGIS Pro project, the top 2 are 2 jpgs with exactly the same export settings. The map is OK.