<p>My new Ender 5 Plus' Bowden tube keeps popping out of its socket on the extruder mid-print, I've tried several times and it keeps doing it even though it's locked into place securely at the start every time. Is this a known issue? And how do I resolve it?</p>
<p>I just got it so I doubt it's the coupler, I replaced it with a spare as my first solution, I did notice that it got almost stringy plastic around it whenever it gets popped out.... could that be indicative of what the problem is?</p>

The coupler for the Bowden tube is probably worn out or the tube end has been scraped so that the coupler can't grab it or you have left out the clamp on the coupler.
The coupler has a sleeve that when pressed down releases the Bowden tube.  There is a C-shaped clip that should go between the top lip of the sleeve and the body of the coupler that prevents the sleeve from moving and should help hold the tube more firmly.  Make sure this is installed.
If the tube outside is visibly worn with scrape marks (this is rare), it might help to cut a few cm off the end so that a fresh section is gripped by the coupler.  Be sure to cut the end flush so that there is no gap between the heat break and the Bowden tube or you will have other problems.
Alternately (and this is more likely), the coupler itself is worn out, possibly with bent or broken-off teeth.  If this is the case, you will need to replace the coupler.