My testing website is suffering from TTFB speed fluctation which i belive is caused by OpCache, When OpCache is turned off the TTFB speed become steady between 1500-1700ms however if i turned it on TTFB speed drop to 800ms however on first visit it always spike to 2100-2700ms. To explain it better if i opened the website homepage TTFB become 2100-2700ms but if i reload the page it drop to 800ms.. and i clicked a link to visit a new page witing the website, its TTFB is also ~800ms.. but if i closed the browser and opened it again and visited the homepage it spike again to 2100-2700ms... I can confirm that its not caused by Page caching or Browser caching.
I though that increasing the OpCache memory can solve that issue so i increased it from 128 to 512mb but it didnt solve the issue.
This is the homepage im testing its speed https://bonmedico-health.com/bonmedico/
and this is the php info and at the buttom of this page i echoed the OpCache Configration and status array if this can help. https://bonmedico-health.com/info.php