Are you sure you are opening the correct PLA file?
Maybe you have saved it in different locations and only think you have the correct one (I know I have done this).
Saving as a PLA and overwriting should have saved your changes - I can't understand why it didn't unless as I say you saved in one location but are looking in another.
As Eduardo mentioned saving as a PLA does not save the PLN which is why you were prompted to save your changes on closing.
It is wise NEVER to ignore that message unless you know you definitely don't want to save.
If in any doubt save it anyway or at worst cancel and 'save as' (check the file type is set to PLN) and save it in another location and/or different name so at least you know you have the latest changes somewhere.
Once you have saved as a PLN then every save from then on will create a backup file BPN (unless you turn the default setting of in the Work Environment).
What you save will become the current PLN and what was the old PLN will become the BPN - which can be opened just like a PLN file.
Saving as a PLA does not give the option to create backups.
Barry.
One of the forum moderators.
Versions 6.5 to 27
i7-10700 @ 2.9Ghz, 32GB ram, GeForce RTX 2060 (6GB), Windows 10
Lenovo Thinkpad - i7-1270P 2.20 GHz, 32GB RAM, Nvidia T550, Windows 11