Welcome to the forums 
@Bazingaa.
I don't have an RT-AX68U, but many of my customers do.  There are no issues reported with 386.7_2 that I have had to respond to (over 35 upgrades from 386.5_2, 386.7, and a few from the beta/alphas).  Most of these are 'dirty' upgrades too.
If your network is not stable after flashing 386.7_2, then I would suggest a full reset to factory defaults (using as many methods as possible), with not reusing any amtm USB drives and testing at least with a minimal and manual configuration to secure the router and connect to your ISP.  Do not take anything for granted, if in doubt, don't enable/disable that option/feature.  Furthermore, note that toggling features and options on/off is different from leaving them as-is after a full reset.  This may be one reason your router/network isn't stable anymore past the firmware you're using.
HTH.