This issue just began to occur in the past few days. The Title Alignment value for the Image visual renders correctly in PBI Desktop but not in the Service. When the Title Alignment value is set to Center, the title text is NOT centered over the image, nor is it centered to the width of the object itself in the Service.
The screenshots below illustrate the difference between how each image title is rendered in the Desktop vs. the Service. I added a border to each image to make the issue more noticeable. Although the Title Alignment value for all the images is Center, and the alignment renders correctly in Desktop, the title appears left-justified in the Service.
If you use custom visual,i would suggest you contact the author to reflect the issue.You may find the visual's information from here.
Based on my test,i cannot reproduce the same issue.I would suggest you update the desktop version and check it with google browser to check if it still reproduces.