Elon Musk is on his longest stretch without posting on Twitter in nearly five years, a nine-day hiatus that comes in the midst of tumultuous efforts to complete his planned $44 billion deal to buy the platform.

The billionaire chief executive of Tesla Inc. TSLA, -1.76%  last posted on June 21, marking Thursday as the most extended silence since October 2017. Normally a serial tweeter, he hasn’t gone more than six days without tweeting since January 2018, according to a Wall Street Journal analysis of tweet data. Since then he has taken a few four-day breaks, most recently this past January, the analysis shows.

Musk’s break from Twitter follows a recent period in which he was especially active on the platform, with a steady flow of posts about the deal, in which he has talked about his criticism of the company and its policies as well as his plans. Of the 10 weeks with the most tweets from Musk since he joined the platform more than a decade ago, five have come since April 1. Musk’s large stake in Twitter Inc. TWTR, -1.08%  became public on April 4, and he reached his deal to acquire it on April 25.

It couldn’t be determined why Musk, who runs Tesla and SpaceX, is missing from Twitter. He has long used the platform as a main channel of communication on a range of subjects, from rocket launches by SpaceX, to a question about cheese, to expressing opinions on U.S. politics. Unlike most other users with large followings, he often reacts or replies to posts from others.

Musk’s team has told people involved with the Twitter acquisition that he has been less available recently because he has been dealing with personal issues, according to a person familiar with the matter.

An expanded version of this report appears on WSJ.com.

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