Japanese table tennis columnist, Jota Ito, commentary on Hina / Miwa situation:
卓球コラムニストの伊藤条太さんのYahoo!ニュースのコメントが確認できます。各分野の専門家や有識者が個人として意見や提案を寄稿しています。
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The fact that treatment was administered by Hayata's physical trainer, Mr. Oka, is within the discretion of the tournament's doctor, and therefore not a problem under the rules. That said, while Mr. Oka is not a table tennis expert, he has recently served as Hayata's bench coach, and it is understandable that Harimoto's doubts could be understood as he could provide tactical advice. Normally, Harimoto would receive advice from his own bench coach during interruptions, so the playing conditions would be equal. However, since this was a match between Japanese players, the absence of either bench coach, as is customary, created a sense of unfairness. I feel that this is an opportunity to consider revising this practice. Regarding the lack of explanation from the umpire, I would like to add that the application of medical timeouts is only communicated by the head umpire; umpires are under no obligation to provide explanations. At international tournaments, the best practice to prevent trouble is to refrain from performing any duties other than those required.
https://news.yahoo.co.jp/articles/f7f28dccf2195fba5a2c7725de742d46bd1fb33e