It was not the reporter. But this prompted me to see if any external plugin is causing the lagging.
Although, I tried this before it turned out that installing one or both of the following plugins will cause Glyphs to lag -
I tend to use ShowCrosshair everyday and I hope it gets fixed, but I am more happy that Glyphs is back to normal.
In addition to that SuperTool by Simon Cozen is causing Glyphs to crash upon trying to exit the program. This was not related to lagging, but still a bummer.
After more extensive testing/work I can say that the lagging issue still persist, but has diminished greatly with the removal of the aforementioned plugins. Currently, I am not sure what is causing it. But a more stable version of text preview will be greatly appreciated.