Help with my Thai Con

Can anyone tell me what's going on with my Thai con and how to fix it? She's been repotted recently but it was happening a little before that. I just checked the roots and they all seemed pretty healthy to me but I sprayed it with hydrogen peroxide/water just in case of rot. She's near a sunny window plus a plant bulb for extra light. What am I doing wrong?? Only the white parts are going brown. The brown parts are still floppy and not crispy at all. She seems happy otherwise since I just got a new leaf that is totally fine. The fenestrated leaf is the second newest leaf I got about a month ish ago.