Diagnosis
The IR sensor on the TV is either obstructed, getting weak, or there's interference from other light sources. It's rarely the remote itself dying first.
How to Fix It
Check for any obstructions directly in front of the TV's bottom bezel where the IR sensor is (a small dark plastic window). Move any soundbars, decorations, or dust. Then, check the remote's battery compartment for corrosion on the contacts (a white/green powder). Clean it with a cotton swab and a tiny bit of rubbing alcohol if needed. Finally, replace the batteries with brand new ones, even if the old ones 'test' okay in another device. The remote needs a strong, clean voltage.
If That Didn't Work
Strong ambient light, especially from direct sunlight or some LED bulbs, can flood the IR sensor. Try changing the lighting in the room or closing blinds. As a last resort, you can use the 'Hisense RemoteNOW' app on your smartphone as a temporary WiFi remote to confirm the TV itself is working fine.
Heads Up
If the remote only works when pointed at the TV's screen and not the bezel, the IR receiver behind the little window is likely failing. That's a main board repair. A universal remote set to Hisense codes is a cheaper fix.