all my miners always start their mining cycles again at the beginning whenever they get a new value (or even the old value) again that tells them what to mine.
as far as i can tell, that is not a new problem, but happens with (almost?) all of the miners that i saw (including a year ago, and on many different versions and savegames). it currently happens on all six of the obsidian miners.
by restarting their cycles from scratch, any mainloop shorter than is needed for a single ore (2.4 to 10 seconds) will not produce anything.
my solution last year was to calculate the mining time and not disturb them during that time. but that made my reaction time to "mining nodes dry" sluggish, especially when they switched targets by themselves.
The "miner-hounds" next to this setup are currently paused while i am testing the miner-buildings. they have my solution ("link SIGNAL to the miner") to avoid that other problem that i often had: miners switching targets after they moved, eg to deliver a full inventory. my current use for all those bot miners (with such links, and with manually specified targets) is to get rid of nearby nodes that are in the way of having a 2x2 or 3x3 node, or a line of nodes, to then be mined automatically.
surprisingly, all my miners that use such links and get their targets manually or by radar etc, don't have the problem of restarting their cycles all the time, but whenever i try to do it by program (either directly with "set to component" or like in the case of the obsidian miners, by using program registers and links) problems happen.
