Hi Michel,
Did you deployed a ring topology (so a loop) on purpose? if so, mostly independently by the uplinking method (single link or aggregated links) used between your three Switches, you should have enabled and configured STP (possibly RSTP) in all of them assigning a Spanning-Tree priority of 0 (maximum) to the Switch you want to act as STP Root and lower priorities (such as 8, default) to remaining two Switches.
Each logical Link Aggregation Group (LAG) interface (made of multiple physical interfaces aggregated together) partecipates to STP and so there aren't issues on that side (all physical interfaces aren't blocked by STP)...if possible use LACP in order to benefit of resiliency and throughput enhancements it provides.