QGIS - couldn't load plugin "processing" - cannot import "bytes"

Question

I just tried to update QGIS, and now get two errors.

This when I open the app

enter image description here

And this when I try to access the processing plugin.

couldn't load plugin 'processing' 
 
ImportError: cannot import name 'BYTES' from 'psycopg2._psycopg' (C:\OSGEO4~1\apps\Python37\lib\site-packages\psycopg2\_psycopg.cp37-win_amd64.pyd) 
 Traceback (most recent call last):
 File "C:/OSGEO4~1/apps/qgis/./python\qgis\utils.py", line 312, in loadPlugin
 __import__(packageName)
 File "C:/OSGEO4~1/apps/qgis/./python\qgis\utils.py", line 737, in _import
 mod = _builtin_import(name, globals, locals, fromlist, level)
 File "C:/OSGEO4~1/apps/qgis/./python/plugins\processing\__init__.py", line 25, in 
 from processing.tools.general import * # NOQA
 File "C:/OSGEO4~1/apps/qgis/./python\qgis\utils.py", line 737, in _import
 mod = _builtin_import(name, globals, locals, fromlist, level)
 File "C:/OSGEO4~1/apps/qgis/./python/plugins\processing\tools\general.py", line 32, in 
 from processing.core.Processing import Processing
 File "C:/OSGEO4~1/apps/qgis/./python\qgis\utils.py", line 737, in _import
 mod = _builtin_import(name, globals, locals, fromlist, level)
 File "C:/OSGEO4~1/apps/qgis/./python/plugins\processing\core\Processing.py", line 54, in 
 from processing.algs.qgis.QgisAlgorithmProvider import QgisAlgorithmProvider # NOQA
 File "C:/OSGEO4~1/apps/qgis/./python\qgis\utils.py", line 737, in _import
 mod = _builtin_import(name, globals, locals, fromlist, level)
 File "C:/OSGEO4~1/apps/qgis/./python/plugins\processing\algs\qgis\QgisAlgorithmProvider.py", line 66, in 
 from .FieldsCalculator import FieldsCalculator
 File "C:/OSGEO4~1/apps/qgis/./python\qgis\utils.py", line 737, in _import
 mod = _builtin_import(name, globals, locals, fromlist, level)
 File "C:/OSGEO4~1/apps/qgis/./python/plugins\processing\algs\qgis\FieldsCalculator.py", line 42, in 
 from .ui.FieldsCalculatorDialog import FieldsCalculatorDialog
 File "C:/OSGEO4~1/apps/qgis/./python\qgis\utils.py", line 737, in _import
 mod = _builtin_import(name, globals, locals, fromlist, level)
 File "C:/OSGEO4~1/apps/qgis/./python/plugins\processing\algs\qgis\ui\FieldsCalculatorDialog.py", line 50, in 
 from processing.gui.PostgisTableSelector import PostgisTableSelector
 File "C:/OSGEO4~1/apps/qgis/./python\qgis\utils.py", line 737, in _import
 mod = _builtin_import(name, globals, locals, fromlist, level)
 File "C:/OSGEO4~1/apps/qgis/./python/plugins\processing\gui\PostgisTableSelector.py", line 32, in 
 from processing.tools.postgis import GeoDB
 File "C:/OSGEO4~1/apps/qgis/./python\qgis\utils.py", line 737, in _import
 mod = _builtin_import(name, globals, locals, fromlist, level)
 File "C:/OSGEO4~1/apps/qgis/./python/plugins\processing\tools\postgis.py", line 24, in 
 import psycopg2
 File "C:/OSGEO4~1/apps/qgis/./python\qgis\utils.py", line 737, in _import
 mod = _builtin_import(name, globals, locals, fromlist, level)
 File "C:\OSGEO4~1\apps\Python37\lib\site-packages\psycopg2\__init__.py", line 68, in 
 from psycopg2 import extensions as _ext
 File "C:/OSGEO4~1/apps/qgis/./python\qgis\utils.py", line 737, in _import
 mod = _builtin_import(name, globals, locals, fromlist, level)
 File "C:\OSGEO4~1\apps\Python37\lib\site-packages\psycopg2\extensions.py", line 37, in 
 from psycopg2._psycopg import ( # noqa
ImportError: cannot import name 'BYTES' from 'psycopg2._psycopg' (C:\OSGEO4~1\apps\Python37\lib\site-packages\psycopg2\_psycopg.cp37-win_amd64.pyd)
Python version: 3.7.0 (v3.7.0:1bf9cc5093, Jun 27 2018, 04:59:51) [MSC v.1914 64 bit (AMD64)] 
QGIS version: 3.8.3-Zanzibar Zanzibar, 685d8b15d2 
Python Path:
C:/OSGEO4~1/apps/qgis/./python
C:/Users/stuar/AppData/Roaming/QGIS/QGIS3\profiles\default/python
C:/Users/stuar/AppData/Roaming/QGIS/QGIS3\profiles\default/python/plugins
C:/OSGEO4~1/apps/qgis/./python/plugins
C:\OSGeo4W64\bin\python37.zip
C:\OSGEO4~1\apps\Python37\DLLs
C:\OSGEO4~1\apps\Python37\lib
C:\OSGeo4W64\bin
C:\OSGEO4~1\apps\Python37
C:\OSGEO4~1\apps\Python37\lib\site-packages
C:\OSGEO4~1\apps\Python37\lib\site-packages\win32
C:\OSGEO4~1\apps\Python37\lib\site-packages\win32\lib
C:\OSGEO4~1\apps\Python37\lib\site-packages\Pythonwin
C:/Users/stuar/AppData/Roaming/QGIS/QGIS3\profiles\default/python

Answer 1

Regarding the processing plugin, in my experience sometimes the path gets messed up. You could try to simply uninstall/reinstall the processing plugin using the plugin manager.

Another thread you could reference seems to explain that this happens commonly when running 2 versions of QGIS: Missing Processing Tools in Vector Menu of QGIS?

• Stuey17: Processing is a core plugin so I can't uninstall. The problem feels like its coming from the path / having 2 versions of QGIS.
• Erich Purpur: This is a somewhat dated thread but shows you the path of the processing plugin: gis.stackexchange.com/questions/175636/…