perhaps it is a problem in the SNAP configuration. Please, could you check the values in [YourPathInstallationFolder]/etc/snap.conf and snap.properties?
In the first you will find a line similar to:
default_options="–branding snap --locale en_GB -J-XX:+AggressiveOpts -J-Xverify:none -J-Xms256M -J-Xmx5G
the Xmx value is the maximum RAM memory used by SNAP, try to set it as high as possible considering your system characteristics. In the example, I have set 5G in my PC of 8G of RAM.
In snap.properties you will find the value snap.jai.tileCacheSize. Depending on your processing, the best value can be different, but you can try to set it at 70% of the value selected for Xmx.
If it was working properly in your previous installation, then you can try to set the same values (if you still have them).
On the other hand, I see in your screenshot that you have made some operations and then you open the output band. SNAP is not doing the computation of previous step until you open or save the images, so you have to have into account that during “creating image…”, all this computation is made so it is normal that it takes some time.