Horizontal black lines after saving as TIF

I normally download JPG files from my camera, open them in Photoshop Elements, then immediately save them in TIF format for later editing. Over the years this has worked well through various versions of Windows and Elements. But in the last few weeks the TIF images have been marred by several fine black horizontal lines. On screen, the lines appear and disappear as the magnification is changed with the mouse scroll wheel, but they invariably appear on the print. The problem occurs whether I use PE10 or PE13. My OS is Windows 10 (32 bit), and I have found the same problem if I use Irfanview for the file conversion. I have also tried converting to other formats such as PDF and BMP, but either the lines are still there or PE cannot open the file.

I have been unable to find an explanation or solution on line, but by trial and error I have found a work-around that works - by selecting  the "Per Channel" option during the conversion to TIF instead of the default "Interleaved", ignoring the warning messages.

My questions are: (1)What causes the problem and is there a better solution my work-around?

(2) Why has it appeared only recently - is a Windows update responsible, and if so which one?