A couple thoughts come to mind. If the tank vent is not working properly, it will create a vacuum in the tank as fuel is used by the trimmer. Once that vacuum is high enough, it will prevent the trimmer from properly drawing fuel into the carburetor. When the vent (usually a duck-bill valve built into the fuel cap) is working properly, it allows air to be brought into the tank when enough vacuum is created to overcome the resistance of the duckbill vent. To test if this is your problem, loosen the cap on the fuel tank when it is exhibiting the issue and see if the problem goes away.
The second thought is potentially an ignition problem that only occurs once the unit is hot.

Okay I will get it out tomorrow and try loosening the cap when it starts to happen, thanks for the advice.

Check the exhaust to know it is clean and not causing any back pressure (that might cause it to run hot).

Also! Check your spark before you start and check for it after it stops.

Okay I was finally able to replicate the problem after weeks of having it run fine. This time the trimmer didn't last long, started and about 2 mins into it died. I loosened the gas cap and nothing, even took it fully off at one point with low gas and had it tilted and still died on full throttle. I also heard an audible metal on metal clinking that I hadn't heard before. How exactly to I go about checking the spark? Also, I visually checked the exhaust, but is there a more thorough way to do it? I'm pretty unfamiliar with this stuff....

I have three weed wackers, none purchased by me. One Echo salvaged on trash day. And a battery Craftsman and a gas Yard machine given to me.

While I am not the best person to give advice about precise repairs and fixes for weed wackers, I would like to throw my two cents in on tools in general.

Most of the time you get what you pay for. I would only buy a chainsaw from Stiehl or HuskyV.

And I would probably avoid the low-end trimmers, and buy a battery model or a model from Echo, Stiehl,etc.
I have never had a Ryobi trimmer, but have had a number of Ryobi products. Frankly I don'tknow how good the Ryobi drills and other tools are because the battery always goes bad after three years or so. It makes sense to upgrade to another package (say 18V instead of the 14.4) instead of buying more overpriced batteries. So I never really get to test how well the tools hold up.

Anyway, just wanted to say you might consider a battery type trimmer next time. Or become a cheapscape like me and let others buy the tools, and then try and fix them.