Artifacts appearing

Hi guys, I'm having some trouble with some artefacts apprearing, don't even know why. I exported the video and it was all fine, then the next day I went to edit the same video and noticed there's these colourful artefact on the footage. I think it is the blur effect, when you add that to the text. See examples below.
Please help. Don't know what to do.

Thanks in advance.
Best wishes
Rubin