Red line and slow playback with no obvious reason

Hi all,

I'm currently experiencing a red line and very slow playback at my place of work and there is no clear reason why.

My sequence settings match the clip settings (I choose this when dropping in the footage) but still get a red line at the top of my timeline and limited playback.

We work off a large server and when opening the same projects on any other colleague's computer they have a yellow line above their timeline and a far faster playback speed.

It also appears to seriously slow down my export speed, with 7 min edits taking over an hour on my machine but under 10 mins on others.

I've explored the best possible project settings to use and had my Macbook Pro completely wiped, nothing seems to solve the problem. What's particularly confusing is that although it seems like it's probably a project issue - it can't be, because the exact same projects don't have this problem on anyone else's Mac.

If anyone has any ideas that could solve this or have experienced anything similar, your help would be much appreciated as it significantly slows my editing speed and limits the proficiency of my edits.

Thanks in advance, Carl