Tried to fight world boss and left area to repair gear. Could not re enter fight for some reason. Could do that the day prior in the beta. Now I can not earn the mount trophy. Why could I return to town the day prior and still return to the boss but on the last attempt of the boss in the beta I can not do that? There was only 10 people on that boss. Now how am I supposed to get this trophy?
Yesterday? You may be a bit confused.
there it is corrected.
Blizzard made this weekend to screw payers. End of story. Very few people got it. Many have refunded over it.
So im sorry but you are screwed like 90%+ of the player base. Oh and did i meantion blizzard enjoys this part?
The rules were very clear and leaving to repair your items takes you out of the instance. Going back does not guarantee that you will be able to join that instance or any other for that matter.
Given that it was the last spawn for the beta, many people hellbent on getting it, so it is very likely that all instances were full which is why you did not get put back into it.
There is a cap how many players can be in a single instance and when you step out regardless if you teleport or walk out, there is no placeholder for you, somebody else took your spot.
You should have stayed and tried your best to dodge, this concept will apply to future bosses too. You cannot hold your spot in an instance if you are not there, so keep that in mind next time. 
The thing is the instance wasnt full.
Have you thought about it this way:
Let’s say maximum number of people is 12 in a single instance.
Your instance had 8, which gives 4 other players room.
You leave, so now there’s 5 empty spots.
But given that it is the last spawn, people that were late also went there filling up spots so by the time you repaired your stuff and went back, you were placed into an empty instance which was generated after the spawn, which is why no monster was there anymore.
very much doubt that it was filled. People were giving up mid way through the timer since the boss was at 2/3 hp.
You’ve convinced me, your game was bugged.
Not wanting to rub salt in open wounds, but are you sure there are so few players who have gotten the Ashava Trophy ? Because my kid and me both separately from one another managed to qualify at least 3 times out of 5 times that each of us did the Ashava event.
I am not saying we were so good ourselves, certainly not, but we did our part, we kept at it, tried to get behind her or under her even when our gear was at 0% and the group we were in still managed to defeat Ashava. That was 3 out of 5 times that both of us tried it and yes, I have also one time like you dared to try and go back to town quickly to repair my gear, but only once and that did threw me back to another event where Ashava had already been slain and there was no stuff for me to pick up. So, I am kind of doubting the claim that not many players got the trophy. Surely, we could not have been that lucky, even though we played ferociously fanatic - hunted down all the beta goodies and put in loads of hours, or could we ?!?
I mean whose to say you were just fortunate to have competent players when you did it? 
It does no good when players have no idea what they are doing.
It is unfortunately that you had to encounter those then. It is what it is then. But I do understand your aggrevation.
If you left the encounter to go repair your gear, you would be ported into a new instance of the encounter (most likely a healthier one than you had left). This is to keep the players who aren’t contributing from getting fat loots.
See that wasnt the case before when leaving other times when doing the boss. Was always able to re-enter the instance when I left to repair gear.
So you’re a repeat offender, leaving someone else to do the work while you collect the reward. At least you admit it, but this is probably the exact reason it works now the way it works.
You see, the more people in the zone (up to 12 I believe), the harder the boss is for everybody. So if you are not contributing to the fight, you shouldn’t be in the fight. You’re a leech at that point.
So its better to be dead weight with broken gear doing 1dmg then leave for a few seconds to repair gear to actually contribute? You contradict yourself. 
If you have nothing to contribute just leave the topic.
That’s not at all what I said. What I said is, if you’re dying so much your gear is broken, you clearly aren’t contributing and should leave the fight. That is why when you port back, you’re in a new instance.
Yeah really contributing to figuring why my game bugged out.
If you were having technical difficulties or just didn’t have any gear, you weren’t contributing either way and therefor just making the encounter more difficult for everyone else. It can be frustrating having lag issues to be sure, but that’s neither here nor there.
again you failed to read my original problem.
if you have nothing to actually figure out my problem just leave please.
Since I cant reply anymore to thread will do so here
“Next time when ashava spawn how about come prepared?”
I did come prepared.