Syncing, Synchronizing
noun
You're making things in two different places be exactly the same for a period of time. You're in the middle of a process called syncing. You can see 同期中 a lot in computery contexts, or if you change your device language to Japanese. (Not that I recommend that...)
どうきちゅう
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.
ごめん、今データ同期中だからちょっと待って。
Sorry, I'm currently syncing data, so please wait a moment.
Dropbox、いつも同期中にフリーズしちゃうんだよね。何でだろう。
Dropbox always freezes during syncing for some reason. I wonder why.
昨日はGoogleドライブがずっと同期中で午前中仕事にならなかった。
Yesterday, Google Drive was syncing all morning, so I couldn't get any work done.