Opus Directory stuck when previewer opens big text files

I have Previewer open for most of the time when I browse through the files, it constantly causes for Opus Directory being stuck when it tries to preview big text file. It's not possible to cancel or finish the preview, I have to stop execution through Task Manager

How big is big? How many lines and what file size?

Which viewer/plugin is handling the files? (It should say next to the filename, at the top of the viewer pane after the file is loaded.)

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