The tile says No comp
Synapse works in the active composition. Click into a comp’s timeline or viewer so it’s active, then select its layers.
The tile says Select 2+
Synapse needs at least two layers to link. Cameras and Synapse layers don’t count. If you selected a Synapse and only one other layer, Synapse says Select two or more layers · Shift-click to add to Synapse, because a plain click makes a new Synapse. Shift-click to add to the selected one instead.
On a Shift-click it means no layers besides the Synapse were selected. Synapse says Select layers to add.
The tile says Max 40
Web links up to 40 layers at a time, which is already 780 pairs. Select fewer layers, or use Chain or Hub for the rest. The same limit applies when Shift-click Web would bring a Synapse past 40 layers.
The tile says Linked
A Synapse in the comp already has exactly these lines, so Synapse doesn’t stack a copy. On a Shift-click it means every line you asked for is already in the selected Synapse. When linking two stars it means those two are already linked.
The tile says No Synapse
Shift-click and Alt-click work on a Synapse. Select the Synapse layer along with your layers. Shift-click can also find the Synapse on its own when the comp has only one, or when one of the selected layers is already in one.
The tile says Locked
The Synapse you’re adding to or removing is locked. Unlock it in the timeline. Removing several Synapses skips the locked ones and removes the rest.
Some Web lines are missing
Web shows a line only while its two layers are closer than Max Distance on the Synapse effect. Raise Max Distance, or move the layers closer. The sky and the counts show only the lines in reach at the current time, so the count changes as your layers move. The lines past reach are still stored and come back when the layers drift close again.
A line doesn’t show at all
Check Draw On and Width on the Synapse effect. Draw On at 0% or Width at 0 hides every line. Inset hides a line whose layers are closer together than twice the inset. A Synapse layer that’s hidden or sits below an opaque layer won’t show either.
The lines are on the wrong layers
Synapse names each linked layer in its expressions. When a layer’s name is shared with another layer in the comp, Synapse refers to it by its place in the layer stack instead. Reordering the layers then points those lines at whatever layer is now in that place. Give the layers unique names before you link them, or remove the Synapse and link them again.
The Synapse shows an expression error
A linked layer was probably deleted. Undo the delete, or remove the Synapse and link the remaining layers again.
When Synapse can’t set its lines up in the first place, it says Synapse lines couldn’t follow their layers with After Effects’ reason, and leaves the comp as it was.
Adding to a Synapse in a duplicated comp
A duplicated comp’s Synapse keeps working on the copied layers. Shift-click in the copy adds to that copy’s Synapse and keeps all of its lines.