Dell claims to be unaware of this issue that they have had for years. At the least, Dell should provide a Material Safety Data Sheet to those with the problem. Totally unacceptable. 

Does anyone have any info on what this substance is? Is there any way for the problem to be fixed? My AIO is fully functional with “leakage” issues.

I think this substance is the glue that glues the LCD panel to the glass digitizer. My Precision 5720 is having the same issue where the LCD panel is separating from the digitizer glass. I suspect the system is running hotter than usual and these systems are notorious for getting  hot because their heat sinks are not seated properly even when new.

I absolutely agree. I thought it was just a problem that I had in Hong Kong as the temperature in the summer can get quite high. I had no idea that this was a global and not just a tropical problem. I came back from a long trip to find a puddle of clear goo at the bottom of my AOC. I did not suspect anything toxic but I have young kids walking around my workspace all the time.

I have similar issues with 5720 aio. LCD  is separating from digitizer glass. And after 4-5 month my entire screen went blank. I connected via hdmi to external screen to check if it works fine and it did, so inbuilt screen is dead now. I will never buy sub par quality dell AIO again.

I bought my Precision 5720 AIO touch screen since 2018 and started having issue on 2020 with my touchscreen software so they had to uninstalled this function and that same year I started noticing bubbles on the screen, but didn't care until now is almost all over the screen specially on the edges and yes a puddle of glue on the desk that is way to sticky to get rid off. I will try to see if customer service has any input on this issue and also if I can find info about, so I can circle back here.