Update 7/17
Arrived into Downtown Disney just after 815am. This time took the Monorail into
Disneyland. As soon as I entered the station, I purchased G+.
My goal was to FISH in the morning, while riding a few non-LL attractions, and then return at night to use MEPs in Fantasyland.
I booked Indiana Jones LL, but as I was on the Monorail, I noticed Matterhorn was down (app did not show it being down until a few minutes after). I was able to book a LL for the Matterhorn with a return time of 835am.
My MEP did not switch over, and the Matterhorn came back on line around 840am. That sucked.
So I booked my go to attraction, Indiana Jones, for 845am (refreshed a few times). By 9am Indiana Jones was down. Once I got the MEP, I booked IJ again with a return time of 930am-1030am. IJ still down, got my second MEP. Tried to do it a third time, but IJ came back up, so I switched to Big Thunder.
Went in to Stand By for Big Thunder, then Jungle Cruise (horrendous 10 minute posted wait turned into 30 because they had 3 boats online, but were training CMs with one boat, and were still working on getting more boats online), then rode Pirates.
Left the park around 11am, Big Thunder eventually went down, got my 3rd MEP. While at home, I just continued to scan and book IJ or BT for the rest of the day. I was never lucky enough to get a 4th MEP. However, I booked a legit Space Mountain LL for 730-830pm
Came back into the park around 730pm. Used my LL for Space Mountain (10 minute wait), had some dinner around 8pm. 830pm walked by Rise, decided to use LL on Falcon. Didn't need to, as Falcon was a complete walk on. Even though the posted wait time was 35 minutes. Booked a LL for Mansion next.
After Falcon grabbed my Tatooine Sunset at Rontos, then went back to check on Rise. Line still showed 55 minutes, but didn't seem to be moving, so I decided to skip and instead use LL for Mansion while Fantasmic was playing. Again, I didn't need to use LL for Mansion, even though posted wait time was 25 minutes.
As the fireworks started, we headed to It's a Small World, Walk On Wait. Then grabbed some popcorn and watched the Encanto show on Small World.
NOW ABOUT THE MEP and FANTASYLAND experience (note this is what happened to me, it can differ for others)
By this time it was about 10pm, I walked over to Alice in Wonderland, and CM said it wasn't ready, even though there was a significant queue.
Decided on Pinocchio, no wait, did not use MEP.
Then we decided to test MEP on Peter Pan (app says not allowed). I went to the CM near the disabled area, didn't say a word, showed them my MEP, she "scanned" it, and I was let into the queue where the ramp leads up to the boarding (5 minute wait). Checked the app while in line, even though scanned the MEP was still there.
Went to Mr. Toad next, showed the CM working the unloading area my MEP. She did not scan and just let onto the next vehicle. Maybe a 2 minute wait.
Went to Snow White after that. This time I was scanned in, BUT again the MEP still stayed in place.
Then did Carousel and Casey Jr next maybe 5 minute wait.
Went to Alice, but the line for disabled was super long, so we decided to skip.
So to sum it all up, I had 3 sets of MEPs. Not once did the scanning process take away any of the 3 MEPs I held.
AGAIN, this happened to me on 7/17. There is no guarantee this will happen for anyone else, BUT there should be good info to know if people want to use MEPs for Fantasyland attractions.