I have a large QGIS projekt with about 50 layer, several of which are QuickMapService Base maps or other WMS-Layers. I work with this project for over a year now and had no problems.
I run QGIS on a Manjaro-Linux platform. Recently my QGIS was upgraded to 3.12 against my will and was very unstable afterwards. I reinstalled the LTR 3.10.6 from the AUR. Since then the following problem occurs very frequently.
I can load my project without issues and work for a while, but when zooming QGIS appear to have issues loading the maps. The map window turn blank and the status bar indicates constant activity, for as long as you want to wait. Neither raster nor vector data are rendered. When trying to close QGIS it indicates, that a process is still running. When restarting QGIS, the project works fine until the issue starts again.