How do you navigate between cells in tables?

I have been using the tab key to navigate to the next cell in a table (or to create another row at the end of a table) and that was working perfectly, but suddenly it stopped working. Now, if my cursor is in a cell, if I press tab, it starts moving through the menu options on the left side of the screen instead of just navigating to the next cell in the table. The arrow keys don’t work either. 
I have tried looking it up and I’ve tried everything I can think of to make this work and I can not get the tab key to navigate me from cell to cell anymore. This makes the table feature nearly unusable because you have to manually use your mouse to navigate to the next cell, and that’s not realistic. 
Is there some setting that I accidentally turned off that stopped the tab key from navigating within the table?