My project has gone too deep and I can’t share it… But after trying many times (re-launching Dorico, opening other files, etc…), I found that the “Add Bar Number Change” method worked briefly once on my troubled Dorico project, and that helped me eliminate the forced bar number change from the imported Sibelius file. However because there are several more forced bar number changed later in the file, I was presented with the same problem again. Then I accidentally found that I could select the forced bar number and delete, just like what Daniel suggested (before I saw his reply) … I just need to zoom in close enough to be able to highlight the number and I could delete it, then the bar number becomes continuous again, which is what I want. So my problem is now solved!
However, I feel that there seems to be some issue with “Add Bar Number Change” feature for imported Sibelius file (that has forced bar number changes), because on my other files entered entirely in Dorico, I have no issues at all with “Add Bar Number Change”.