You don't actually have a solar bypass, in a true sense. So you were misinformed. Refer to the drawings I did for you. I'm assuming all those valves are still in the same position as photographed.
Water leaves your filter and enters the solar valve where it is blocked by the current position of the valve and sent to the left, into a tee fitting. The water tries to go both up and down the tee. The water going up runs into the solar check valve and can't get past that. So it goes down, on to your heater, and then into the pool.
If the solar valve is turned, the water would then go up from the solar valve, but is currently being blocked by the solar isolation valve. I cautioned you about being sure not to engage the solar system, or allow the solar controller to do so, because the closed solar isolation valve would then deadhead your main pump and that is bad.
So technically the solar valve is "bypassing" the solar system, but a true solar bypass valve is a separate thing, used for a separate purpose, and you don't have one of those. Now if your "someone" stating "no longer good" was referring to the solar valve, or the solar check valve, and either of those is not effectively stopping the water from going up, then that would be a big problem and could explain why your pool is half empty.
I was going to get to that... Once you raise the water level 6" or so,
with the pump OFF, and pause a bit to make sure it doesn't leak back down, then fill the pool. Then start your pump and see if water comes leaking or spewing out of either of the cut off PVC pipes up by your roof. Those steps will determine a lot. Report back here when you do those three things.
So, for future reference:
All PVC ball valves are junk. You have at least three that I can see. The solar isolation valve is a PVC ball valve. As are the two near the ground that look the same (red handles). All junk. In fact, the two near the ground serve no purpose, other than negative ones. If either is closed, you'll deadhead your pump. And one or both will eventually start leaking. All three should be removed and replaced with PVC pipe.
While I probably shouldn't declare your solar check valve as junk, it probably is. It's a cheap version of one, anyway. You need a proper Jandy check valve at that location, and a second one between the filter and the solar valve. You could replace the ball valve after the filter with a proper check valve and solve both of those problems at once. A Jandy check valve is a high quality component, it's repairable, and it has a clear cover that allows you to not only see if it's working or not, but also allows you to see water flowing through it. They look like this:
Or you could install a Jandy check valve in place of the solar check valve, and a FlowVis in place of the ball valve after the filter. That would allow you to fine-tune your solar heater's efficiency. I can explain more about that some other time, if you're interested in that topic. You can retrofit a FlowVis onto a Jandy check valve body later, as an alternate option. A FlowVis is a check valve, so it serves as both a check valve and a flow meter.
So you've got some tasks. Fill the pool 6", confirm it's not leaking, then fill the pool 100%. Start the pump and report back here with what happens.
Later, perhaps if you reinstall the solar system, swap out the three PVC ball valves and the PVC check valve as described above.
