Memory issus with only 4000 members

Hello,
I get that error when I click on "members". I wait 45sec and then :
Fatal error: Allowed memory size of 268435456 bytes exhausted (tried to allocate 72 bytes) in /home/stb03410/public_html/system/modules/core/drivers/DC_Table.php on line 5497
That error came after I import 4000 members.

I've checked the memorylimit in phpinfo() : memory_limit 256M
I've reduced the number of elements shown in the configuration (30 instead of 500)
The size of tl_member in phpmyadmin is 90MB
I deactivate the modules I've developpped to be sure
Contao version 3.5.3 (updated with live update)
The driver is mysqli (default)

Could someone tell me where is the problem ?
Thank you

Probably within Contao itself. Maybe you should create an issue on GitHub.