What would cause an elastic pool to exhibit high "Sql Server process core percent" metricsj, but low DTU / CPU
So DTU actually combines three different things into one (CPU, Memory and Disk) and even with Disk you get a fixed Disk Size but also a max limit of IOPS and Throughput. I would recommend to check all these metrics out and see what all of these are showing you. Also look at connection failures other connection related metrics as well. For a time trend average stat is a good view but for a time period when you would like to know what happened at that minute then look at both average and max.
More details on DTU model can be found here.