Updated description by @unknown
Steps to reproduce
Load the attached test world,
Press the button labelled "run test."
Expected result
Each detector rail detects the minecart coming onto it and powers the adjacent redstone lamp.
Actual result
Only the detector rails in the same chunk as the minecarts detect the minecarts and power the lamps.
Original description
The rail system is close to the same, but the detector rail is not being activated on one side (as indicated by one being lit up and the other not being). The system is around the same on both sides I repeat so I do not know what is the problem with this, but if one side seems to be working, why not the other? When it goes uphill, it stops there and the piston blocks it; however, the piston blocks it the same for both sides but does not activate the rail equally. If there needs to be more information on what I am building, I can provide the scenario but it is regrettable it does not work. Let me know if you can look into it. If you need to reproduce the problem, build an upwards track both aligned along the x-axis, and send one going upwards negative and the other positive, and the detector rail on the bottom (not to mention it is blocked with a fence or piston above the flat detector rail) will not activate one of the rails. To give an even better representation of this problem, I recreated the exact problem along the x & z-axis (can't do that y-axis because the game doesn't work like that).
[media]
While I was trying to fix the build of a system of Redstone, I found the exact direction of the railway to work apparently. However, I noticed the other railway built before still wasn't working. As I continued my quest for answers, I found this happening on the screenshot below that is the most recently added. Two identical railway systems pushed into the ends of them with only one turning on and the other still not on. I am more baffled at this.
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Confirmed and updated description with steps using test world. Turn out the issue is not due to the direction the minecart is coming from. Instead it is due to the detector rail being on a chunk border and the minecart coming from the neighboring chunk.

I was going to suggest or comment if it was a chunk bug and it seems to be that way with your confirmation, but as I didn’t know the exact problem, I didn’t feel confident enough to make such an assumption. Got any more comments if it’ll be fixed or if it’ll have to stay like that due to some restriction?

Oh you're fine, I'm happy to help with figuring these kind of things out. The information you provided was sufficient for me to go on to suspect a bug and have an idea of what to test.
The bug tracker staff are volunteers and don't have direct contact with the developers. We don't get updates on the tracker about planned fixes, schedules or prioritization, sorry. Since I've confirmed the report, it will be forwarded to the developers' internal tracker at some point. Generally speaking, reports are prioritized by votes and impact.

1.19.20 too
From the pictures this look looks like a bug in the detection range of the detector rail along one axis, although it could be related to the hopper minecart collision box as well. I will update the report again when I have tested it.