Dredging up an old thread, but I think OP is right about there being a bug?
Just got my A4mkii, was playing around with arp legato, and unless I set the arp len parameter to a huge (or inf) number, it cuts off after one or two notes of the arp. (it’s unpredictable, like at arp speed 3 it plays one note; at a slower arp speed 5, it did 2 notes)
Note length is much longer than the arp speed (speed 2 or 3, note length 8). Amp envelope is a full-sustain envelope, so it’s not that.