If that was the case I feel like it would say it at least? Plus Slowed is a condition usually imposed by spells and stuff, I'm not exactly sure why being encumbered would reduce your AC or make you not use reactions e.t.c. Hopefully it's just there and I've missed it somehow.I don't see it either. There is a bit about speed dropping to 5 if you are trying to push drag or lift too much on 404 & it mentions 616 there on the left but 616 is an appendix A start & image. With it not even being listed in the appendix maybe it imposes a different condition like.... and it should say "If you exceed your carrying capacity, you are encumbered (see Appendix: Conditions on page 616)."?
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