I am not sure of the calculations behind the Bridge tool to advise why it works in some scenarios and not others.
I have attached 4 methods I often use which gives the same result as what you're trying to achieve with the bridge tool, hopefully one of them assists you.
[Method 1]
1. In EDGE Mode, SHIFT + DRAG an edge to create a new edge
2. Newly created Edge
3. With the Newly created Edge still selected, click COLLAPSE
4. In VERTEX Mode, click TARGET WELD and weld the vertice to close the Triangle
[Method 2]
1. In FACE Mode and with SNAP 3 selected, click the CREATE button and click all 3 triangle points
2. Face has been created
[Method 3]
1. In EDGE Mode, click both edges and click the BOX located next to the BRIDGE button
2. In the BRIDGE TOOLS adjust the BRIDGE ADJACENT parameter until face has been created
[Method 4]
1. In this scenario switch to BORDER mode and select the Triangle Edges
2. Click CAP to create the missing face
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Technical 3D Graphic Artist
Autodesk 3dsMax 2015 - Service Pack 4
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