Troubleshooting in this order:1) Pull out oven and fridge to look for more downstream GFCI outlets I may have missed.2) Check the voltage coming from my hot line to make sure it is 120.3) Disconnect the upstream outlet and retest the hot line downstream to confirm it is actually downstream and not getting extra voltage from somewhere.4) Replace the down stream outlet with a regular old outlet.5) Make sure everything is wired correctly at the devices in question.6) Admit defeat and call a professional.Thanks for all your help.

For this company I'm a technical consultant meaning I help clients run projects through our system as well as do troubleshooting & answer questions regarding the product we have.

part of your responsibility is at move in to show them how things work,, how to turn on the heat, how the smoke detector works, how to provided a toilet plunger with the apartment so if they have a minor toilet clog they can fit it themselves,, and show how to use it, where the electrical panel is an how to reset a breaker,.... the stuff ordinary people would understand but renters aren't always ordinary people.Get a system for contact for repair requests,, have them text or leave on voice mail ,, don't go and answer each call right off the bat,, give a thought... call back and try and trouble shoot with them over the phone... as for toilet and drain clogs I'd let them know if plumber comes out for service if it is found that clog is from food, toys in toilet,, or grease they will be charged a service call. some use a form for this at move in. 

Not sure if the issue is with LastPass, Android, ATT, or HTC.Maybe I'll just join the one-world order (apple) because freedom of choice, ability to expand, and need to troubleshoot is just too difficult to handle  ;)

Or trouble shoot a software issue when AI fails? 

Also, I would like to just be more knowledgeable in general about my personal rentals, how to troubleshoot issues (plumbing/electric/etc) instead of just relying on what a handyman tells me.

So far, I do the following for tenant reported issues (learned from BP & elsewhere):Tenant sends me a pic of the issueI try to troubleshoot via email, or go take a lookContact handyman if I can't solve and send them the picHandyman contacts tenant to schedule appointmentHandyman sends before/ after picsI mail handyman a check for completed workKeep in mind that I developed a relationship with my ex PM.

Most of the issues I have had with furnaces are largely operator error and troubleshooting is quite easy 

@Nathan Adams, if it were my property, I'd have a licensed electrician go in and trouble-shoot. 

If you have time, YouTubing to DIY and trouble shoot building issues can save you a lot of cash for your next purchase.