How much data are you trying to replicate?
The maximum amount is 65.536 bytes if I remember correctly.
There is also a limit for the maximum array size, which is also 65.536.
If you are below these values, it might be that you have not configured your project to make use of the maximum values.
There are two settings in the ProjectSettings → Engine → Network called “MaxArraySize” and “MaxArrayMemory”.
You could turn those up to max.
Alternatively, add the following lines to your DefaultEngine.ini (this is the same as doing the configuration via the Editor’s ProjectSettings):
[/Script/Engine.NetworkSettings]
net.MaxRepArraySize=65535
net.MaxRepArrayMemory=65535
If the issues is that you are above those limits, then you won’t be able to use the built in replication system (at least I don’t know of a way to go beyond the limits). You would then have to either extend the existing system by replicating your data in smaller chunks or build your own system.