Specified cast is not valid..

I am just using a table visual to show data stored in oracle table, which has about 20 columns. I pulled in 10 columns which includes some decimal data type columns, but after that from the remaining columns when I try to pull in decimal columns I get below error

Product Version:
2.88.1144.0 (20.12) (x64)

Error Message:
Specified cast is not valid.. The exception was raised by the IDataReader interface. Please review the error message and provider documentation for further information and corrective action.

OS Version:
Microsoft Windows NT 10.0.18363.0 (x64 en-US)

CLR Version:
4.7 or later [Release Number = 528040]

Peak Virtual Memory:
38.6 GB

Private Memory:
846 MB

why is this happening ? I never encountered this before