According to security firm Vanguard, the IMO and UKMTO:

• 6 vessels were hit on Sunday - the most in a single day since the conflict started
  4 vessels were hit on Tuesday
  2 seafarers are reported missing and a container ship reportedly sank

Iran first targeted merchant vessels transiting the strait in March, in retaliation for US-Israeli strikes on its territory. Tehran has continued to strike vessels using routes it has not approved.
The strait is normally one of the busiest routes for oil and commodity exports from Gulf countries, and the attacks have disrupted shipping.

Key context:
23 attacks recorded since the start of October, almost double the average monthly number since the war began.
The US said Saturday it struck a cargo vessel as part of its embargo on Iranian ports, but that incident was not listed by the IMO.
24 seafarers have died near the Strait of Hormuz since the start of the conflict, according to the IMO.

Vanguard analyst Barun Gupta said the rise may be linked to a recovery in Gulf oil flows, which had recently returned to about 80% of pre-war levels before falling back again. By increasing attacks, Tehran can show it can still disrupt that recovery and impose costs on shipping and global energy markets.
Gupta also cited President Trump's promise last week not to launch further attacks on Iran before the US midterm elections, giving Tehran "a perceived window to increase pressure with a lower immediate risk of US military escalation". (Bssnews)