centered graphics are left aligned after epub export

Using Windows 11, current version of InDesign.
Trying to complete the digital/ebook version of a book.
First, I’m not new at this. Been writing and doing my own publishing for 37 years. I have never had this particular glitch before.
No matter what I do, all my centered graphics are left-aligned when exported to epub. The exact same file does fine in both 8x10 and 6x9 print versions, using all the same graphics and settings.
Object styles are used for all graphics.
I’ve tried using other graphics I’ve used many times before with no problems, and graphics I’ve never used. Same result.
I’ve tried resetting the default graphics style, even creating a new one.
I’ve tried using a new template, both my own, and ones offered in ID panel.
I’ve closed ID and reopened. 
I’ve rebooted my computer.
I’ve checked for updates on PC and in Adobe CC.
I’ve rolled back InDesign to previous version (as suggested repeatedly on various forums and help sites). This did not change the problem. Graphics are still left-aligned.
I’ve copied one of the print versions and pasted it into a fresh template. Same problem.
I’ve created a fresh document and inserted placeholder text and various graphics, including and omitting the original graphics in my file. Graphics are still left aligned.
I’ve exported the digital file to PDF, and the problem DOES NOT HAPPEN. Graphics are centered in pdf.
This may have no bearing on the issue, but I did uninstall the beta version of Photoshop just before this started happening. Other than that, I cannot figure out what’s causing this.