There are a number of similar posts e.g. see this one Unconfirmed transaction after 4 days; getting worried which may help you out.
The issue is that there are 197 inputs for this transaction and some of the miners limit the number of inputs they will accept (via -mempooltxinputlimit). Most notably Flypool, that controls the majority of the hashrate, which in that other thread appears to limit to 150 inputs. Some of the other miners don’t have this limit so it’s possible it will be mined when one of these other miners finds a block but you might have to be patient.
See here New Release: 1.1.0 - Electric Coin Company and the -MEMPOOLTXINPUTLIMIT DEPRECATION section, this problem has been addressed but it isn’t going to solve your immediate issue as Overwinter doesn’t activate until late June.