mprowe There is a problem with AC3s not respecting a user-set battery reserve greater than 4%, which is reported to be one of the bugs fixed in the beta about to be rolled out as production firmware.
@Britkat is doing a sterling job of developing and maintaining GivTCP and while he and his collaborators understand what the issues are and what they are fixing, IMHO it's a tall order for Givenergy staff to also be on top of those issues as well as the ones which fall within their responsibility.
Had you done the old Reset to defaults, it should have put the inverter back into a state where the ECO/Timed charge modes should work as designed by Givenergy and you would have been able to identify something in the GivTCP automation as the culprit.
I'm not intending to criticise what you did, rather summarise for the benefit of others, what might have been a short-cut to identifying the cause of unexpected behaviour. Thanks to the collective knowledge on this forum regarding the intricacies of GivTCP when being used to control the inverters, the issue was resolved in the end.