Lowrance-Master/Slave is in affect if your units are networked. In other words, you need to power up the unit Guide Lanes were imported on first.
HERE'S THE COMPLEX ANSWER for LOWRANCE users:
RULE#1:
Waypoints, Routes and Trails are maintained in a UDB database on each unit. With multiple units you have multiple databases and when the multiple units are ethernet-connected you have ONE MASTER UDB and multiple SLAVE UDB's. The MASTER maintains waypoints between all units. Trails are not maintained or transferred between units.
RULE#2:
The MASTER UDB is the 1st unit to be powered on. All the remaining network-units become SLAVE UDB's. If the MASTER is powered-off or rebooted, the SLAVE's will negotiate a new single MASTER.
RULE#3:
ALL WAYPOINTS, ROUTES AND TRAIL IMPORTS ARE ONLY DONE ON THE MASTER UNIT'S UDB. IF YOU IMPORT ON A SLAVE, THE SLAVE WILL TRANSFER THE USR OR GPX FILE TO THE MASTER.
So following the above rules:
The Simple Import:
You import your SD-card into the MASTER. The USR or GPX data-file data is imported into the MASTER's UDB. The MASTER transfers waypoints, but not trails to all the SLAVES. So the SLAVES have none of the imported trails.
The Misunderstood Import:
You import your SD-card into a SLAVE. The USR or GPX data-file is transferred to the MASTER unit(rule#3). The MASTER unit imports transferred data-file into the MASTER's UDB. The MASTER transfers waypoints, but not trails to all the SLAVES. So the SLAVES have none of the imported trails. Thus the SLAVE unit you are using "appears" to only have imported waypoints.
Import Consideration #1(Importing Trails):
Trails do not transfer from MASTER to any SLAVE. Trails can only be imported onto a MASTER, hence common practice is to only power-on a single unit and perform the import. Do this individually on each unit where you want the trails.
Import Consideration #2:
USR version 5 and after introduced data UID(Unique Identifiers) for waypoints and trails. UID's better identify data. Better prevent duplicates.
Import Consideration #3:
USR version 5 and after because of UID's often import faster especially when merging with existing data. Merging can painfully slow down an import.
Import Consideration #4:
Importing GPX file data into existing data is notorious for creating duplicate waypoints.
Lowrance Trails:
Some say trails, some say tracks. Lowrance absolutely has better trails than HB and Garmin. Trails can be used for boat-runs, road-beds, creeks and etc. I'm not a route fan because of all the extra waypoints.
Lowrance trails support track-segmentation. HB does. Garmin does not.
HB Solix has the very dangerous "track-point scrubbing", other HB products are spotty.
Lowrance trails use much fewer track-points, thus much more efficient.
Lowrance trails always display at all zoom-levels even if the 2 track-points are miles apart. HB does not. I don't know about Garmin.
The best waypoint manager:Reefmaster Waypoint Manager for LowranceDon't tell Lowrance, keep it quite:
Lowrance can support more than 300 tracks, not the documented 50 maximum.