Error in nagvis after upgrading Ubuntu to 20.04 (LTS)

Just a quick update, after update to 1.6.0p21 (CEE) problem is still the same. NagvisExceptionHandler throws this in WebUI:

Error: (0) in_array() expects parameter 2 to be array, bool given
URL: /cdp/nagvis/frontend/nagvis-js/index.php?mod=Map&act=view&show=BRZ
File: /opt/omd/versions/1.6.0p21.cee/share/nagvis/htdocs/server/core/classes/GlobalMapCfg.php
Line: 1028
#0 [internal function]: nagvisExceptionErrorHandler()
#1 
/opt/omd/versions/1.6.0p21.cee/share/nagvis/htdocs/server/core/classes/GlobalMapCfg.php(1028): 
in_array()
#2 
/opt/omd/versions/1.6.0p21.cee/share/nagvis/htdocs/server/core/classes/GlobalMapCfg.php(488):                 
GlobalMapCfg->checkMapConfigIsValid() 
#3 /opt/omd/versions/1.6.0p21.cee/share/nagvis/htdocs/frontend/nagvis-
js/classes/NagVisHeaderMenu.php(164): GlobalMapCfg->readMapConfig()
#4 /opt/omd/versions/1.6.0p21.cee/share/nagvis/htdocs/frontend/nagvis- 
js/classes/NagVisHeaderMenu.php(305): NagVisHeaderMenu->getMapList()
#5 /opt/omd/versions/1.6.0p21.cee/share/nagvis/htdocs/frontend/nagvis- 
js/classes/NagVisHeaderMenu.php(82): NagVisHeaderMenu->getMacros()
#6 /opt/omd/versions/1.6.0p21.cee/share/nagvis/htdocs/frontend/nagvis- 
js/classes/FrontendModMap.php(117): NagVisHeaderMenu->__toString()
#7 /opt/omd/versions/1.6.0p21.cee/share/nagvis/htdocs/frontend/nagvis- 
js/classes/FrontendModMap.php(80): FrontendModMap->showViewDialog()
#8 /opt/omd/versions/1.6.0p21.cee/share/nagvis/htdocs/server/core/functions/index.php(120): 
FrontendModMap->handleAction()
#9 /opt/omd/versions/1.6.0p21.cee/share/nagvis/htdocs/frontend/nagvis-js/index.php(53): 
require('/opt/omd/versio...')
#10 {main}

In Apache Error.log the following:

[Tue Feb 23 09:19:52.662758 2021] [fcgid:warn] [pid 13308] [client 127.0.0.1:44678] mod_fcgid: 
stderr: PHP Deprecated:  join(): Passing glue string after array is deprecated. Swap the parameters 
in /opt/omd/versions/1.6.0p21.cee/share/nagvis/htdocs/server/core/defines/global.php on line 41, 
referer: http://CHECK-MK-SERVER-IP/cdp/check_mk/side.py

Martin