Are you a member of a local astronomy group? You have suffered long enough and it sounds to me as if this needs an experienced owner to locally assist you 'hands on'. I was driven nuts for some weeks. It is a steep learning curve and Celestron instruction manuals are awful. But most problems are entirely due to use data input error.
It would help if you listed your equipment in your Cloudy Nights signature as I have had to read the entire thread to fathom that out. Even so, I am confused as you now mention trying Starsense. Do you own Starsense or are you simply set up with Nexstar HC + alongside SkyPortal external WiFi accessory and tablet? For that, I assume you are using Android (Samsung) tablet?
It is probably time for back to basics to discover by a process of elimination where the nuisance lies.
The 6SE can be controlled by various different devices (there are others)...
1. Nexstar + HC or Starsense HC (with Starsense camera)
2. SkyPortal external WiFi accessory and APP (SkyPortal or SkySafari) for IPad or Android.
3. Celestron CPWI for Windows 10 laptop.
Each of 2 or 3 simply replace (1). Using various combinations we can work out where any glitch might lie.
Suggest you remove SkyPortal dongle and attempt a Nexstar + Hand Controller alignment to eliminate the mount as a possible cause. Have you tried doing a factory reset on your 6SE?
Have you referred to Mike Swanson's Nexstar Resource website? Read the page on "Possible fixes for Hand Control misbehaviour. That would evaluate problems with your hand controller (and some mount settings).
Have you tried connecting your SkyPortal external WiFi accessory with a Windows 10 laptop running CPWI? If that works, that might suggest a problem with APP/tablet.
I believe (but may be wrong) that I read somewhere that there was a problem with one of the SkySafari versions. Have you tried uninstalling and reinstalling only Celestron's SkyPortal APP (which I found more reliable).
Have you possibly got something wrongly set (example wedge = yes)? Without looking at a screen shot of your APP settings page it is hard to guide you. That's why I think you would benefit from hands on assistance.
In the APP, ensure that <time> is set to NOW and in settings, Time and Location are both = current.
Are you sure that Location Services switched on in your tablet? I had to reset a host of stuff in my Android, including removing battery savers and like nuisances that kept interrupting the APPs. To be frank, I gave up with Android and now use SkyPortal external WiFi accessory in Access Point Mode connected via my network to a Windows 10 laptop running CPWI. Whilst I got SkySafari working, I found it nowhere near as dependable compared to CPWI.