Some users have recently had their accounts hijacked. It seems that the now defunct EVGA forums might have compromised your password there and seems many are using the same PW here. We would suggest you UPDATE YOUR PASSWORD and TURN ON 2FA for your account here to further secure it. None of the compromised accounts had 2FA turned on.
Once you have enabled 2FA, your account will be updated soon to show a badge, letting other members know that you use 2FA to protect your account. This should be beneficial for everyone that uses FSFT.
Sorry, I never tried using the Ergo with the old receiver. This support article talks about pairing the Ergo with BT, but says nothing about BT being always on.
I've been using the MX Ergo trackball since December 2017, also replacing an MX 570. This has been on a Windows 10 PC, without Logitech drivers, and I've been very happy with the trackball.
The Ergo is a more quality build than the 570. It "feels" better in the hand; I'm sure the added weight...