You're hitting this problem because to support fast refresh Oracle will create a multicolumn index on the GROUP BY columns of the MV table, and as the error message says, 32 columns is your limit on that -- I wouldn't categorise it as a bug, but more of an "undocumented implied restriction".

If you're intending on using fast refresh then you may still need a supporting index for the MV -- not neccasarily, but most likely. The index that Oracle creates to so this is based on the undocumented Sys_Op_Map_NonNull() function, to avoid problems with trying to join (actually, MERGE) on nullable columns.

Anyway, you might have a combination of columns in the MV that forms a unique key without having to include the entire set of GROUP BY columns, particularly if some of the columns are hierarchical parents of others. If so then you can just create your own index ... something like ...
Code:
create index my_index on my_table
(
Sys_Op_Map_NonNull(col1),
Sys_Op_Map_NonNull(col2),
Sys_Op_Map_NonNull(col4),
Sys_Op_Map_NonNull(col5),
...
)
You will almost certainly benefit from the index having a compressed structure.

Not a fan of the mixed-case column names, by the way.