No chat history between spark2.6.3 on PC and spark 2.5.8 on MAC


I’m not very tech savvy so go easy on me. Use Spark for work, obviously through a work server which I don’t control settings on. My work computer is a PC, that was installed for me, works fine. I installed spark 2.5.8 on my mac, the only version I could install which seemed to actually work. My full contact list appears, I can start conversations, but none of the conversations that I had even earlier that same day can be found when I login to the 2.5.8 Mac version. Any ideas?