Ok, made some progress and I believe I have identified what is causing the issue. If I disable a password on the WiFi network it works. When i set a password again it fails. The options available on the Deco system are either WPA2 or WPA/WPA2. Have tried both and it fails. No special characters in the password. I believe there must be an issue with the way the Roku Express is authenticating. Since all my other WiFi devices are working with WPA/WPA2 I do not believe this is a TP-Link /Deco issue.
There have been a few known issues with the TP-Link Deco (various models) and Roku devices.
If having trouble connecting the Roku Express (2.4ghz-only Express models like the 3930), either temporarily disabling 5ghz band while attempting to connect or creating a guest network seemed to work best.
1. Temporarily disable the 5ghz band. Connect the Roku device to the 2.4ghz band. Re-enable the 5ghz band.
2. Set up a Guest network for the Roku devices. Most are fine with passwords. If not, disable the password on the Guest network only. WPA/WPA2 or WPA2-only should both be fine. (I generally use WPA/WPA2 so all network devices can connect/fallback connection). If using WPA/WPA2, remember to try and use shorter password. If you prefer a long password, select WPA2.
-----
The Deco mesh routers are not very configurable, so kind of have to use one of the above if you plan on using 2.4ghz Roku devices with it. Have not seen too many issues with the dual-band (2.4ghz and 5ghz capable) Roku devices and the Deco, so may want to consider an upgrade if the above workarounds do not work for you or you find them unsuitable.
