Hello,
You can troubleshoot such link issues to some extent in IMC 7.3 with the Topology Diagnosis. Right-click on one of the devices in the topology and click Topology Diagnosis, it will show you which neighbor-discovery related protocols are running on the device, and which ones IMC is using.
Generally it is a good idea to use only one single neighbor discovery protocol, preferably LLDP, as it usually proves reliable. However IMC will also process CDP, STP and MAC intersections by default, and when they are all running, this can sometimes cause inconsistencies in the link calculation and "fake links". There was also a ProCurve-specific bug where CDP inconsistencies break the algorithm.
Try ensuring only LLDP is running and then synchronizing the devices in IMC.
Under System > System Configuration > System Settings > Layer 2 Topology Configuration is where you can find the settings for the topology calculation. Unless you need them, I would suggest setting STP Link Calculation, MAC Intersection and Inter-Routing Interface Calculation to "No" to prevent them from interfering with the topology (and then synchronizing devices again).
Getting a bit more advanced here, you can also get a full text dump of the topology information IMC knows via System Configuration > Data Collection > check the box for "l2topo" and run the collection, then open the l2topo.txt in a text editor. It will show you a long list of every IMC device and which link information was gathered from which protocols.
PS. There are also some vendors with poorly implemented LLDP-MIBs, so if it still doesn't work correctly, check the SNMP output from the device for that MIB to make sure the device isn't sending IMC something incorrect.