That's the typical behavior of a local mode AP. If it lost connection to WLC it will try to discover another WLC. If it can't using normal methods (DNS, Broadcast, etc) it will try to renew IP & see if it discover a WLC to join. (that's why even AP had static IP, it will change to DHCP & try)
Yes, if you convert this to FlexConnect, once AP lost its connection to WLC, AP will go into a mode called "Standalone" without hunting for an WLC. It will work, but you need to understand differences between these two modes as these mode address specific needs (local mode for standard deployment & FlexConnect for branch deployment).
Refer below for different modes of H-REAP (previous name for FlexConnect)
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