I'm not just the only one having the back plastic cover issue on my A52 or the A72 or any other Samsung Galaxy Ax2 series. The issue is that the back plastic cover on the Ax2 series could come off anytime (especially on the top where heat is rampant) because of bad build quality like weak glue or just a design flaw, could happen randomly if you use the phone without case under sunlight or just by removing the case, the case could grip the back plastic cover and peel it off because the design of the back plastic cover isn't flush to the frame like the A53, Ax3 series which solved the back cover issue, my aun'ts Samsung A72 has a noticeable gap between the frame and the plastic cover on the side where the side buttons are and I advised her to never remove the case or drop it on water, if you use a Samsung A series especially the Ax2 series, I advise you to not remove the casing since you could peel off the back panel. It's a SHAME that Samsung advertised the Ax2 series as ip67 rated when the ip rating is negated by the bad build quality and the design flaw of the back cover, there could be a lawsuit anytime on Samsung about the ip rating or the back cover issue on A series especially when I often see posts about the back cover issue on a Samsung A series (more like A52) subreddit in Reddit and especially here in the Samsung community. I have dropped my A52 once in a bucket of water and it was submerged for a second, the next thing that happened is that the screen was flickering and sometimes didn't turn on because water already seeped inside from the gap between the frame and back cover that peeled because of the weak glue and the bad design flaw, And my mother had to pay for the repair even if the water damage could've been avoid had the people who work on Samsung fixed the issue on the back cover and the build quality on the Ax2 before they even released the new A52 (Ax2) series and advertised it as "ip67", I bet the A51 would've survived being submerged in water despite having no ip rating unlike the A52 which would just get water damaged because of the bad build quality/design flaw even if it has an ip rating. Again, there could be a lawsuit anytime on Samsung regarding this issue, the least that Samsung can do is not lower the value of the A series if it has the back cover issue when trading it for an A54 or A34.
This photo of the A52 having a panel gap is from Reddit.
I have A53 and I also have issue with this. Though not as worse as yours but mine created a small gap. 
