Hi, i am attempting to edit a model i started, but each time i open it it loads with either chunks missing, or is not how i left it off originally when saving it first time round.

Here are some examples:

This is how my model should be on my other side (this side loaded partially correctly, but i'm using it to demonstrate what i mean)

https://imgur.com/cfQhhqL

However, this is how my other side looks: (Notice also where i put the red circle, the line doesn't spread to the other side, which it originally did)

https://imgur.com/XGiab5R

This is how my model looks when i atttempt to re open it:

https://imgur.com/WZrQmWm

Can anyone help me with this please? I can answer any more questions if need be.