Read display errors

Hi. I’ve used an EMClient PRO account without issue for years on a Mac. Two days ago the preview pane and full messages started misbehaving without any seeming cause. The text sometimes overlaps into a mess, or sometimes show as one line stacked into a long column. The pictures don’t display properly at all, sometimes with text/ links overlapping pictures, or sometimes pictures just showing as a narrow thumbnail. I’m on an up-to-date M1 MacBook Air running Sonoma 14.2.1 and there are no other issues at all with the device. EMClient is also up-to-date. The change happened on Wednesday while using EMClient which was working perfectly until the change. I’ve been through all the settings to see if I have inadvertently activated a change through a shortcut but can’t find anything. I’ve currently turned it onto plain text only (which is also too small despite trying to change it in settings) so I can function but it feels like working on an early 2000 Windows device and I really would like to get back to my normal fault free software display. Any ideas? Thank you