LED's draw less current than incandescent's so it sounds more like a short circuit wire causing the fuse to blow.
I would start trying to narrow down where the problem is by removing the two new rectangular fixtures and seeing if the other two remaining fixtures will still blow the fuse. You could either reinstall the old fixtures or just tape wire nut the wiring for them while they are out. If the fuse still blows, you know the problem is related to the wiring / fixtures for that part of the circuit.
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