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
Please help. Don't know what to do.
Thanks in advance.
Best wishes
Rubin