Hello Crinrict,
thank you for caring for my problem!
The time jumping has ocurred 3 or 4 times in recent weeks since the addition of Get Together.
It always happened directly after installing a new patch, so this may be an important clue.
Time jumping always happened when my Sim returned home from a public lot (in my cases night club and café). He jumped to a random time.
Skill points and earned money (in my case from DJ work) were lost, the notifications ("Your Sim earned 12 Simoleons ...") however were still there.
In all cases, other members from my family were at work or school when time jumping happened. They were brought back to my home lot, but their avatars still showed them at work. I could fix that problem by letting them travel to other lots and back. After that the game went back to normal and was not corrupt. Perhaps this is just a glitch caused by the installation of a patch. On the other hand problems with travelling Sims were a main source of disaster at Sims 3. In Sims 4 with all its travelling and loading screens this would be even worse, so EA should investigate the issue.
I have all Sims 4 packs installed and don't use any mods/CC.
My comupter specs: HP Envy, Intel Core i5, Nvidia GTX 760 1,5 MB OEM, 16 MB RAM.
Viele Grüße und ein schönes Wochenende :-)