What seems to have happened and shouldn't is that the texture size stayed at minimum (1x1) instead of being adjusted back to a higher value when you selected High.
To change that, select Preference (Ctrl+P) and then under Real-time Render Options, set Max Texture Size to 1024x1024 or higher:
When I change the Render option from Minimal to High the resolution is adjusted automatically to what it was before at the High setting.
The only thing I can think of is that you inadvertently set the Max Texture Size to 1x1 while High was selected. In that case it would remain at that setting.