The connection between a Front End and a Back End in Access is based on the Server Message Block (SMB) protocol, which is a member of the TCP group of TCP/IP. (The other sub-group is UDP.) TCP protocols in general have message headers that include a sequence number. When a message "skips" a sequence number, it usually indicates that a lower level of the network "hiccuped" and dropped data. This kind of error is signaled to the programs using the network via an error that is essentially, "Path lost to partner." The message you get from Access reflects this situation.
As a precaution, before you continue to use the database, make a quick backup copy and to a "Compact & Repair" operation on the COPY. If it succeeds, make the repaired copy the "live" database and put aside the unrepaired copy. This DOES, of course, require down-time, but it is the safest way to proceed.
You do not usually need to C&R the front-end if the original database split was done cleanly. There is nothing IN the FE that would suffer from a network loss.