Hi Sergio.
You would need to try multiple steps for this to work.
1. If you are able to get the compose screen now (not the white screen of death). You can try the below.
a. Take the backup of the SAP Lumira Documents (found under your documents)
b. and then inside the folder, you would see a file called .uptodate. Delete it and restart Lumira to see if you can update your LUMS file.
2. If you are getting the white screen of death, then try the following.
a. Delete the .sapvi folder found under your profile directory (%USERPROFILE%) and restart Lumira.
Let us know if you solve the issue.
Regards
Shankar