Error in symbols

I'm using ADE for my studies since the study material is provided through this plataform. The issue is that some symbols (specially mathematical ones but not only) are sometimes not shown clearly, as you can see in the picture below.

Strangely I used that book 4 months ago and all this symbols were clear and also the symbols are still clear in the ADE of my work. It must be due to some update or something like this. Could someone tell me how to solve this issue?

Thanks in advance for all your help.