I've just tried your exact example on Win10-64 and MMA 12 and Ta
+ tab in fact autocompletes to Table
in my system. You may try deleting your autocompletion history.
You can find that here:
FileNameJoin[{
$UserBaseDirectory,
"SystemFiles\FrontEnd\SystemResources\FunctionalFrequency\AutocompletionHistory"SystemFiles\\FrontEnd\\SystemResources\\FunctionalFrequency\\AutocompletionHistory.m"}
]