Nice to hear you and your users love this :)

Check xperience.php
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$message = construct_phrase($vbphrase['xperience_gap_text'], $vbulletin->options['bburl']."/member.php?u=".$vbulletin->userinfo['userid'],

how come i have like 250k points yet when i go to the shop it says i have 0 custom points? is that a glitch?

You have 250k EXPERIENCE points, not custom, I guess...

Correct. The currency for the item is set to custom.

how do users get custom points then? i saw on another forum and they somehow had it set to Post points?

You will have to edit the shop item and set the currency on that items to f.e. experience points.
Custom points you get by AdminCP, Experience, Manage Custom Points

Won't you upgrade for 3.8.x to stop decreasing points if I delete posts/threads?

If my forum(s) prunes threads every X days/months, a lot of posts/threads are deleted, so my users are losing a lot of points :(

No chance for this, as this cannot be just changes. The whole core has to be recoded.

Ok, let's be aware to lost points and give those points from admin panel..

Another doubt is that, when I go to Activities --> Shop (name) says "There are no activities yet.", the 60% of articles are sold at this moment...

Cannot confirm this. Please PM me the URL to your board.