I think if you export to crosstab you keep the formatting - in your case with the K or M. If you export the Data you keep the original format down to the decimal places.
unfortunately there is no resolve for this in tableau tools have limitations we need to understand this..
secondly am supposing you are using complex join custom sql..
Use distinct and cherry pick all the fields that are essential for the user business..
this will resolve the issue ..
i face this issue on every new dashboard i develop.. You have to go distinct in your query..
structure your query out calmly you will get it