Unresponsive arrow keys PowerPoint

Arrow keys in MacBook's (Pro mid 2012) keyboard do not advance or go back slides in PowerPoint (v. 15.34) or Keynote (v 7.3.1) when entering presentation mode.

Trouble started after last MacOS (10.13.2) update. Then when MacOS 10.13.3 came a few days later, it seemed to function correctly.

Then again the trouble is back. Enter a presentation in either program and fwd or rew keys DO NOT WORK.

I suppose there might be a conflict between softwares…

Has this happened to anyone?

Hope to find a solution soon...

thanks

larry