Is prayer permissible if the Imam interrupts the recitation at Allah's saying: ﴿that you may reflect﴾ [Al-Baqarah, 219], then resumes recitation in the second rak'ah from the middle of verse 219?

The matter of recitation after Al-Fatihah is broad, and the Imam's prayer is valid even if he omits it entirely. Reciting part of a long verse, such as the Verse of Debt (Ayat al-Dayn), is sufficient to achieve the essence of the Sunnah. There is no harm in the Imam bowing when he reaches the verse: "that you may reflect," as the meaning is complete and pausing there does not suggest a corrupted meaning. This pause is called a good pause (waqf hasan). As for the Imam beginning the next prostration from the middle of the previous verse, it is good, though not obligatory; it is better to start from the beginning of the verse.