Hi  @Irisies3212,

May I know what is the model of your router? You can refer to How to find the model number of your TP-Link device.

There are a few different cases related with unstable connection, including WAN connection unstable and wireless client devices unstable.
For WAN connection unstable (Router Internet LED turns red/orange occasionally): 
    1) Connect a PC directly into your modem to verify if your ISP Internet is stable.
    2) Make sure the Ethernet cable between your modem and the Router is connected properly, replaced old cables with new ones.
    3) Change the DNS Server of the Router, login the web management interface of the Router, go to Advanced > Network > Internet > Advanced Settings, change the two DNS Servers into 1.1.1.1 and 8.8.8.8. How to Change the DNS servers on the wireless router and DSL modem router (New UI)?
    4) Go to Advanced > System > Firmware Update to upgrade the firmware of the Router. How to Upgrade the Firmware on the TP-Link Wi-Fi Routers?
For wireless client devices unstable: 
    1) Make sure the Router is properly placed, it should be put in open area instead of inside a cabinet or shelf.
    2) Login the web management interface of the Router, go to Advanced > Wireless > Wireless Settings, change the wireless channel into another one.
    3) For 2.4GHz wireless client devices, adjust 2.4GHz channel width into 20MHz, for 5G wireless client devices, adjust 5GHz channel width into 80MHz or 40MHz to avoid interference.