You need to know what Version it is, indicated by a V and a number on the back, otherwise, impossible to answer the question for you. you can check the TP-Link download page for your country to see if there is a firmware update for that model, the docs say to make sure to use the download for your region only.

If there is a firmware update, you have to match firmware version with extender version or you can mess it up, so look carefully. Some other models no new firmware was needed, but the rest of the steps to delete the troublesome app, reset the router to factory default, forget all connections on all devices, re-config using web interface only (never again the app), then reboot router via web interface before trying to redo connection to devices, worked for some, though I don't remember which, sorry. Other models only needed firmware update, some needed both.
 

Edit: Nevermind, check this thread for 455:
https://community.tp-link.com/en/home/forum/topic/249556

If that doesn't solve it post there, since it is an appropriate thread for your model. The forum mods claimed it has been fixed (they've said that before), though this time some have confirmed it, it has a link to the firmware for that model. They said they fixed the app also but I'll never be installing that trash again on any device to check.

Good luck!