Do you have a USB game controller, like XBox, connected? If so disconnect it and if that doesn't stop it, reboot. I had the same problem in NEOS, and posted a request on their Discord help channel (having forgetten,) and that fixed it in NEOS also.
No, ao's were disabed, and even with the minimal character test avatar, the jumping still occured. Disabled and stopped all animations, don't use gestures.
Yes, disconnecting keyboard makes no difference. I did do what Lindal suggested, tried both default avatars and the character test avatar, made no difference.
This is occuring in both the official Second Life viewer and Firestorm. As soon as I log in, my avatar starts jumping and I can't get it to stop. RLV is not enabled, and I can't access menus, they just flash and disappear. Thanks in advance! (I can't get a video clip small enough to attach.)
Second Life Release 6.5.1.566335 (64bit)
Release Notes
CPU: 11th Gen Intel(R) Core(TM) i7-11700 @ 2.50GHz (2496 MHz)
Memory: 32441 MB
OS Version: Microsoft Windows 10 64-bit (Build 22000.376)
Graphics Card Vendor: NVIDIA Corporation
Graphics Card: NVIDIA GeForce RTX 3060 Ti/PCIe/SSE2
Windows Graphics Driver Version: 27.20.100.9664
OpenGL Version: 4.6.0 NVIDIA 472.12
Window size: 1920x1009
Font Size Adjustment: 96pt
UI Scaling: 1
Draw distance: 128m
Bandwidth: 3000kbit/s
LOD factor: 1.125
Render quality: 5
Advanced Lighting Model: Enabled
Texture memory: 512MB
Disk cache: Max size 204.0 MB (100.0% used)
J2C Decoder Version: KDU v7.10.4
Audio Driver Version: FMOD Studio 2.01.07
Dullahan: 1.12.3.202111032221
CEF: 91.1.21+g9dd45fe+chromium-91.0.4472.114
Chromium: 91.0.4472.114
LibVLC Version: 3.0.16
Voice Server Version: Not Connected
December 16 2021 09:58:25