I found this article from Reuters to be particularly interesting: Russian toll in Syria battle was 300 killed and wounded
A few key points:
1. The clash was on 7 February near Khusham in Deir al-Zor province in Syria.
2. Last week 300 Russian contractors may have been killed or wounded in Syria.
  a. That would be 100 killed and 200 wounded according to one rumor.
  b. Or at least 80 killed
  c. Or 5 killed according to Russian officials.
3. It is probably more than 5.
  a. The wounded men have been sent to 4 Russian military hospitals.
  b. There were more than 50 patients at one hospital.
  c. There were three planeloads of injured fighters flown to Moscow.
  d. One ward contained 8 patients.
4. The unit was 550 men and there are only about 200 who were not casualties according to one source.
5. They were “contractors” employed by the “Wagner Group.” These guys: https://en.wikipedia.org/wiki/Wagner_Group
….
Related article: Russia: 5 citizens probably killed by U.S. strike