Child being labelled incorrectly.

[Chesterlife]

Wondering for somebodies advice/experience.
I met my partner 2 years ago and his 2 children. Aged,5&7.
I also then met his ex partner.
Since I’ve known my step son he’s had ‘difficulties’going to school not everyday but occasionally where he doesn’t want to go in. He used to cry and refuses to leave his mum. He was labelled with separation anxiety.
Now my partners ex tried to get him diagnosed with autism. Which me and my partner disagreed with. His ex used to say SS had tried to kill himself by jumping down a hill at school. On approaching the school we found out this was not the case and he had simply fallen over. She has continued to say he’s suicidal doesn’t want to be here etc etc. We have my step son on weekends and have never experienced him have meltdown where he apparently bites, kicks, punches screams. He has always behaved and never ever mentioned or said he wants to die.
My partners ex then moved the children’s school and we didn’t see them for a period of time after battling with court etc we managed to get the time back with them. Again at his new school things seemed settled and only occasionally kicked off.
Then we found out that he has started to do things like throw chairs, books, kick, scream bite when going into school. The school confirmed this but said that after 10 mins he calms down and is good during the day.
My partners ex had now said in the last week my step son has stopped eating, smacks his head into walls, shouts and kicks off.
We had the children at the weekend and he ate perfectly and was very well behaved.
We have come to the conclusion it is school related that he doesn’t like going. His ex now wants SS suspended or labelled as adhd to get help.
Camhs didn’t get involved when previously refered.
HOwever me and partner have argued that if he had ADHD he would portray it even at weekends plus when we take him to school on Mondays. Which so far he’s kicked off slightly once when going on Monday but only saying he doesn’t want to go in, not hitting or screaming.
We are really at a loss of what to do we don’t want him being labelled when he doesn’t need to be. We believe this is just a behaviour issue as he’s had to deal with a lot in the past year, new Baby, new school, new house. Etc.
He also gets away with this behaviour at his mums.
Any ideas what we can do?! He’s such a happy boy at weekends I just don’t understand it.

[Mosaic123]

Does your partner's ex have a partner? If so does, he /she get on with DSS? I wonder if he's different at his Mum's home because there is something or someone he doesn't like there.

[Chesterlife]

Yeah she does have a partner. As far as i'm aware he gets along with him. When they come over at the weekend they don't really talk about him or mention anything. About a year ago when the routine for when we had the children was different, when his mum used to come and collect them from ours DSS would run and hide, would refuse to get in the car, say he doesn't want to go back to his mums. (This was before she got a partner). The routine has now changed where we take them to school, so she never comes to get them from the house anymore.
If we ever approach his ex about this she kicks off massively, saying we are lying.