PyQt5 installation results in designer, qtopengl, possibly pyqtgraph errors - pyqt5

Question

I'm having problems with imports, qtopengl, pyqtgraph, and designer version compatibility. Depending upon package installation, either designer will not load custom plugins, with a libQt5Core.so ImportError, or GLViewWidgets fail with QtOpenGl ImportError.
My question(s):
Is there a compatibility problem?
A version problem?
Has anyone resolved either of these issues separately before? I'm not sure if, or how they may be connected.
Is there a way to get both situations working at the same time?
Installation: (python3.6, ubuntu 18.04)
pip3 install --user pyqt5 # -> PyQt5-5.12.2
pip3 install --user pyqtgraph # -> 0.10.0
apt-get install python3-pyqt5
When the pip3 pyqt5 package is NOT installed, designer opens and loads the custom widget plugin successfully. But, running a basic pyqtgraph GLViewWidget results in:
from ..Qt import QtCore, QtGui, QtOpenGL, USE_PYQT5
ImportError: cannot import name 'QtOpenGL'
When the pip3 pyqt5 package IS installed, running the basic pyqtgraph GLViewWidget is successful. But designer fails to load the custom widget plugin with:
from PyQt5 import QtWidgets, QtCore
ImportError: /usr/lib/x86_64-linux-gnu/libQt5Core.so.5: version `Qt_5.12' not found (required by /home/USER/.local/lib/python3.6/site-packages/PyQt5/QtWidgets.so)
Note:
The custom widget plugin is entirely unrelated to GLViewWidget, and the GLViewWidget is entirely unrelated to designer.
The GLViewWidget comes from pyqtgraph, but error is just on import (so far), so pyqtgraph probably is not a source of the problem. Will experiment with this further.
code to try the GLViewWidget
from pyqtgraph import opengl as gl, mkQApp # fails here
app = mkQApp()
view = gl.GLViewWidget()
view.show()
app.exec()
designer plugin minimal example (QVLabel_plugin.py)
from PyQt5 import QtWidgets, QtCore, QtGui
from PyQt5.QtDesigner import QPyDesignerCustomWidgetPlugin
class QVLabel(QtWidgets.QLabel):
pass
class QVLabelPlugin(QPyDesignerCustomWidgetPlugin):
def __init__(self, parent=None):
QPyDesignerCustomWidgetPlugin.__init__(self)
self.initialized = False
def initialize(self, formEditor):
if self.initialized:
return
self.initialized = True
def isInitialized(self):
return self.initialized
def createWidget(self, parent):
return QVLabel(parent=parent)
def name(self):
return "QVLabel"
def group(self):
return "Custom Widgets"
def icon(self):
return None # will raise TypeError in designer, but everything should work fine
def toolTip(self):
return ''
def whatsThis(self):
return ''
def isContainer(self):
return True
def includeFile(self):
return "QVLabel_plugin"
running designer in the directory of the QVLabel_plugin.py
PYQTDESIGNERPATH=. designer
How GL fails:
from ..Qt import QtCore, QtGui, QtOpenGL, USE_PYQT5
ImportError: cannot import name 'QtOpenGL'
How designer fails:
from PyQt5 import QtWidgets, QtCore
ImportError: /usr/lib/x86_64-linux-gnu/libQt5Core.so.5: version `Qt_5.12' not found (required by /home/USER/.local/lib/python3.6/site-packages/PyQt5/QtWidgets.so)

Answer 1

This worked for the "ImportError: cannot import name 'QtOpenGL'"
sudo apt-get install python3-pyqt4.qtopengl
see: Just installed QtOpenGL but cannot import it (from Python)