Replace the splitter and cover if possible. If this is the initial split in the line you want to make sure the new splitter is grounded as well.
Don’t waste your money on repeaters, can you run a coaxial or Ethernet so you can install an Access Point ?
Initial 2 way splitter (ISP in, 1 output to Modem, other output to 3/4 way splitter that feeds the 3 rooms. If you aren’t using the fourth room replace it with a three way. It’s Docsis interfering with Moca.