I use to have a high "Time without a signal" percentage too (50% to 90% range). I tried a TWS fix that works for another android phone to see if it would also drop the TWS percentage on the Optimus. Im not really sure if it fixed it or if it was just a coincidence but now my Optimus is always between 3% and 20% TWS.
You can try the fix I tried and see if you get similar results. Would be interesting to see if it works for you so we will know if it's a legitimate fix for TWS issues on the Optimus.
I used to have perfect signal on my optimus v. In the last few weeks the signal has seemed to weaken to nothing. I cannot get/send calls or messages like before. Surfing the web is terrible. My battery has to recharge daily now.