Crack length of bedroom

[Rick1983]

Hi

Just in the process of purchasing a property that has a horizontal crack running length of bedroom on external wall around 2-3mm
No cracks on exterior. I have a video but can not attach. any help would be greatly appreciated. I have also contacted a structural engineer but haven’t heard back as of yet.

 

[Wayners]

Plasterboard was not stagard when fitting so you end up with a join that spans room in one long line. It's common.
Probably not a joist running along that crack either as they go the other way? Joint has no support so cracked easy.
I used to stick strips of plasterboard over crack on loft side. Fill and tape. Sand and paint. 99% success that they never came back as it's solid when bridged.