Deadlocks happened when massive inserting executed simultaneously in mysql 5.0 - mysql

Question

I am using mysql 5.0 and I met some mysql deadlock problems when there were lots of inserts from different session at the same time (We estimated there would be a maximum about 900 insert statements executed in one second).
Here is the error I got:
1213, Deadlock found when trying to get lock; try restarting transaction
Here is one of my failure insert statement:
INSERT `cj_202203qmoh_prize_log` (`user_id`, `lottery_id`, `create_ip`, `flags`, `created_at`, `create_mac`)VALUES('388','58','???.???.???.???','0','2022-04-01 20:00:33','444937f4bc5d5aa8f4af3d96d31dbf61');
My table definition:
CREATE TABLE `cj_202203qmoh_prize_log` (
`id` int(10) unsigned NOT NULL auto_increment,
`user_id` int(10) unsigned NOT NULL,
`lottery_id` int(10) unsigned default NULL,
`code` int(11) default NULL,
`flags` int(10) unsigned default '0',
`create_ip` varchar(64) NOT NULL,
`create_mac` varchar(255) character set ascii NOT NULL,
`created_at` timestamp NOT NULL default '0000-00-00 00:00:00',
`updated_at` timestamp NOT NULL default CURRENT_TIMESTAMP on update CURRENT_TIMESTAMP,
PRIMARY KEY USING BTREE (`id`),
KEY `user_id` USING BTREE (`user_id`,`created_at`),
KEY `user_id_2` USING BTREE (`user_id`,`lottery_id`),
KEY `create_ip` USING BTREE (`create_ip`),
KEY `create_mac` USING BTREE (`create_mac`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 ROW_FORMAT=COMPACT;
I didn't use transactions at all in my business. Except for the insert statement, the only possible (in fact it's extremely improbable to be executed simultaneously) sql that requires a x-lock executes at the same time is:
UPDATE `cj_202203qmoh_prize_log` SET `code` = ? WHERE `id` = ?;
There are several select statements using index 'user_id' or 'user_id_2' could be executed simultaneously, but they don't need a s-lock.
And same user_id could only be inserted in the same session.
According to my company's policy, I have no privileges to run SHOW ENGINE INNODB STATUS, so I am afraid I could not provide further information.
After I set the transaction level to READ COMMITTED, execute the statement in a transaction and drop both create_ip and create_mac indexes, it seemed this problem have not happened again. But I still couldn't figure out what caused the deadlock.