All done...Unable get lock for processing

When I (phplist 3.6.12) process the queue and click on stop before it is finished, then click on resume, my page is hanging. Forever it seems. I am on SiteGround, I thought it had to do with their server because I saw this in error_log: … Timeout waiting for output from CGI script … after 5 min or so, while php max_execution_time was set to 15 mins.
They reported me the ‘unable get lock for processing’ message wich I never saw (?). That led me to this forum and to “Unable get lock for processing - #9 by jbhunt17
Setting ‘alive’ to 0 fixed my problem. After that I can resume the process and it finishes, sometimes I have to close the window and log into phplist dashboard again. When not hanging I noticed the ‘alive’ field in the table _sendprocess was counting, time I presume. But when hanging this stayed on the same number

Could this be a bug in phplist?