Hi,
a couple of things

a)
>We have contacted the TSO Hosting site and they said it is plugin problem not the server
>But when we tried to login at the times of trouble we had “Internal Server Error”:

an internal server error is exactly that . i.e clearly a server error. (although it might be cause by a lot of things)
i suggest you turn on debug and see what the exact error is (see https://support.wp-pizza.com/topic/how-to-enable-debug-in-wordpress/)

b) the worldpay plugin/gayeway has not changed for over a year so when it suddenly stopped working after 20:00 what (did you / someone) change(d) at 20:00 ? i certainly did not change things…
you should check your mail server settings (though if the order does not even show up in the order history it suggests the email did not (programatically) get send – see debug above as -again – this can be cuased by many many things before the site even gets to try to send emails

c) your setup also throws a bunch of errors
(see /wp-admin/edit.php?post_type=wppizza&page=wppizza-tools&tab=sysinfo)
and a VERY – lets say unusual – session save path (not even sure if this path would work at all.

I am no expert on memcache but am reasonably certain other people use the plugin with memcache without issues

when i say “it will never do that.” i am referring of course to natively implementing it.
i am naturally not preventing anyone from doing such a thing

you should also look at this
https://support.wp-pizza.com/topic/customising-the-css/

i hazard a guess you are not registering when you order with a different email, so you are just a guest and not a known customer

if using the default theme its
.wppizza-article-default .wppizza-article-size:after

if using the grid theme its
.wppizza-article-grid .wppizza-article-size:after

etc (reason being that you will be able to have different layouts for different pages if you want)

there is a min css (wppizza.css) that applies to all and selective overrides depending on layout used

if you want to overwrite things, copy custom.css as outlined earlier somewhere i believe to your child theme and overwrite it as needs be (or use your theme’s inline css option)

wppizza v2x only- something like this perhaps:

add_action('wppizza_gateway_do_order_details', 'my_js_output', 10, 2);
function my_js_output($orderDetails,$id){

print"<script>/* echo your js */</script>";
}

please use your bowsers element inspector to see applied css declarations

your theme already seems to provide an option to overwrite css without having to mess around with files

PS: if your printer adds margins or something , than that’s something i have no control over and you’ll have to speak to the printer manufacturer

why would you be looking at .wppizza-article-image-placeholder
if you want to do something with the shoppingcart image ?

>posts.title.php still is not working in the child theme tree.
works 100% . i can only assume you put it in the wrong directory