Slow editing (time lag)

Hi

I’ve started to write an extensive research report in DT Pro, and as edit I’m facing an annoying time lag - characters showp up slightly delayed after typing them. As part of my text was copied from Text Edit, I converted the whole file (generated first from within DT) into plain text. This didn’t solve the issue though.
I copied the same text into MacJournal, and editing worked just fine.
Any suggestion for troubleshooting? Thanks.