You must have network issues. I run one machine solo with 3 local wallets running at the same time pointed to 3 different ports, 127.0.0.1:8105, 8115 and 8125. I run a second machine solo with 2 local wallets pointed to 8105 and 8125. All 5 miners are scanning the same Burst account.
I also run this same configuration on Burst.Ninja. 3 miners pointed to the pool on one machine and 2 miners pointed to the pool on the other. It can be done, you have to figure out what is going on with your network. I had local wallet syncing issues for awhile I thought about pulling my hair out but I got them resolved over time. When I shut down a wallet that is showing up to current block, I copy the 2 files in the db folder to a backup folder so if in the future one wallet forks or gets stuck I load the known good backup db and get it going again. I haven't had to do that in a few weeks though.
When solo mining I monitor Burst.Ninja on a web browser to see if my miners are on the right block. Burst.Ninja is by far the most reliable pool in the system, IMO.