Very Slow TTFB - Website Load Speed Problem

[Mehdiben]

Hello !

I'm facing a serious website loading issue for my Shopify website.
Store : www.luxsofmorocco.com
My website doesn't always load on time: Sometimes, it may take up to 15-20 to load (usually the first load) ==> TTFB problem.
I tested my website with https://www.webpagetest.org/ which lets you run several tests at one time. I requested 4 tests and below are the results

RUN #1 ==> SUPER SLOW

RUN # 2 ==> NORMAL

RUN # 3 ==> ALSO NORMAL

RUN # 4 : SUPER SLOW AGAIN

You can see that the problem is random and that in 50%, it takes forever to load.. and this is for all my website pages

From what I read in the forum, it may be caused by a code problem in the theme (might by a very large loop) but I'm not sure this is the problem.
On your end it may load quickly on the first try but when you load it multiple times through a 2-3 minutes period, you notice the problem, and the test pretty much show it..

Please if anyone has a clue, I would like your help...

Thank you