EX7700 Firmware 210

I had similar issues - had the extender ( EX7700 with latest 210 firmware update automatically added) working with my ISP router and had username/password issues or unable to obtain IP address error message on several devices, including laptop, iPhone, android phone, fire tv stick (logged in fine initially and good connection/speed, but after a short while connection would drop and any attempt to join the wifi again would come up with message saying username or password incorrect, or unable to obtain IP address).

I had tried turning off the smart connection with separate 2ghz and 5ghz bands, and noticed that the issue then only occurred to the 5ghz band login.

I then tried using the extender with a Netgear R8000 router - initially had the exact same issue when using the "smart connect", so again turned that off and separated the bands, and again noticed this only impacted the 5GHZ extended connections.  Tried several other tips/advice found on this forum (e.g. resetting both extender and router, updating firmware via main admin console rather than nighthawk app, changing bands (and also trying the two separate 5GHZ bands to extend given these are tri-band).  Still no good.  (Just adding this all here as I'm sure others will have followed this around the houses too.)

Then found this post, and rolled back to firmware 206 - went to Download area for EX7700 and found previous firmware version 206 (https://www.netgear.com/support/product/EX7700.aspx#Firmware%20Version%201.0.0.206); downloaded to laptop; logged into EX7700 via the IP-address (can look IP address up on the router attached devices list - I couldn't always get the mywifiext URLs to redirect properly); turned off the "auto update" on the firmware area; uploaded the firmware 206 manually and let it update.  

Since restarting all of the username/password issues and/or unable to obtain IP address have been resolved - I've been running this now for a couple of weeks so pretty sure the 210 firmware is the issue here and as with other posts here, hope for next firmware update to address this.  I have not turned on Smart Connect again as yet, but might give that a go in the future - for now, I've got used to having the separate bands and allocating the fixed position devices (e.g. Amazon Echo Show/Dots, FireTVSticks) to 5GHZ and the mobile devices that are more likely to be in weaker signal spots like in the garden on the 2GHZ;  might also allow me to get clearer signal when all the family are doing their thing on the more default 2GHZ band with their devices.

Using: R8000 router, R7700 Extender and R7000 Extender (in outbuilding)