have you checked your debug.log ?
https://docs.wp-pizza.com/troubleshooting/

>tried to deactivate some plugins
you should be deactivateing *ALL* non-wppizza plugins and use a default theme and check if you can reproduce this

how did you determine that this is related to the wppizza plugin ?

In any event, wppizza uses the standard wordpress registration process.
There are lots and lots of plugins on wordpress.org that would let you tweak the registration process to your liking.
It’s not really anything that wppizza does or controls

works just fine here
tried de-activating all other plugins using a default theme ?
do you still get the same issue if you do that ?

the number of search results per page is controlled by the theme (or indeed by wordpress itself using 10 as a default i would guess). wppizza does not control this.

I am quite sure though that there are probably some filters you could use to adjust this as you like
the reason why you get 10 and 6 results is (most likely) that you have 16 search results but your theme will simply only display a max of 10 per page so the 10+6 would be expected
if your theme were to show 5 per page, you’d probably get 4 pages with 5, 5, 5 and 1 result

you could use the [wppizza_dbp_map] shortcode which does that and more
see here: https://docs.wp-pizza.com/developers/?section=delivery-by-post-zipcode

or add your orderhistory shortcode somewhere and setup the address as outlined here (which will make it a link)
https://docs.wp-pizza.com/shortcodes/?section=admin-orderhistory

or filter your emails like so (adjust as required)

add_filter('wppizza_filter_template_customer_section','my_email_template_markup', 100, 4 );
function my_email_template_markup($section, $template_type, $template_id, $order){
if($template_type == 'emails'){
$field_id = 'wppizza-dbp-map-location';
$section[$field_id] ='<tr><td style="text-align: left; padding: 2px; white-space:nowrap; vertical-align:top;">'.$order['customer'][$field_id]['label'].'</td><td style="text-align: right;padding: 2px;;"><a href="[some link to some mapping site with the address/apikey/etc  added as necessary]">'.$order['customer'][$field_id]['value'].'</a></td></tr>';
}	
return $section;	
}

>Do you know why it is happening?
No, as it works just fine here and without seeing what you’ve done, i cannot comment any more really

PS: if you tell me for what purpose the amount needs to be modified I *might* be able to suggest something (but it entirely depends on what you are trying to do)

Maybe this is of use
https://www.wp-pizza.com/downloads/wppizza-shipday/

>…..where I can see and change my address, phonenumber etc.
but that’s already built into wordpress itself and plenty of plugins exist to customise this too….
maybe I am missing something ?!

I dont think i understand.
there isn’t really any “wppizza custom environment” so to speak.
any additional wppizza data of a user is added to the “normal” WP user data (if enabled in wppizza -> order form)