Could be that your CPU is very slow.
Bitcoin Core, for example, has hard coded hash value of a block at certain height that it assumes is valid, so it doesn't need to verify the transactions up to that point. This value changes with each version.
You might have just hit that limit and your CPU is clogging up now, since it started to verify it.
That could be the case with some really old or weak CPUs, so check your CPU performance with a Task Manager.
I bought a new server with powerful hardware and again the synchronization stopped at 81 percent (448195)
why??
update:
I restart daemon and sync was start...
but in error log i see: [2018-09-25T08:51:07.545Z] error: RPCError: Bitcoin JSON-RPC: Work queue depth exceeded