I tested my unit by not letting it go to sleep but turn it off when I finish reading. On turning it on again, I was able to read, use the dictionary, change the dictionary without problems.
The issue seems definitely related to going to sleep or waking from sleep.
I'm not convinced it is a Ram issue, because if that was the case, I would have had problems while using it the way I was doing these last days.
I suspect that while my unit was rooted, a malicious app that I might have installed could have modified something not in the system or data partitions because if the problem was there, then the restore set, combined with a factory reset would have solved the issue.
So by exclusion I suspect that that the presumed malicious code lies elsewhere. The question is, in which partition? And therefore, is it possible to copy this partition from another PRS-T1?
Any help is mostly appreciated.