LPA prevents log in: what could be the reason ?

Our server runs on 4.0.7. On a Sunday the server starts writing:

2015-01-31 21:51:12,418 [      LPA Change Event Monitor] ERROR com.ibm.team.lpa.http                               - CRJCA0043E A Lifecycle Project Administration request could not be completed on this host: https://svljazz02.svl.ibm.com:9450.
>>> GET https://svljazz02.svl.ibm.com:9450/jts/service/com.ibm.team.repository.common.internal.IFeedService?maxResults=1000&since=2015-02-01T04:46:09Z HTTP/1.1
>>> Accept: application/atom+xml
>>> Cache-Control: no-cache, no-store
java.net.SocketTimeoutException: Read timed out
    at java.net.SocketInputStream.socketRead0(Native Method)
    at java.net.SocketInputStream.read(SocketInputStream.java:140)
    at com.ibm.jsse2.b.a(b.java:18)
    at com.ibm.jsse2.b.a(b.java:226)
    at com.ibm.jsse2.SSLSocketImpl.a(SSLSocketImpl.java:120)
    at com.ibm.jsse2.SSLSocketImpl.a(SSLSocketImpl.java:454)
    at com.ibm.jsse2.f.read(f.java:15)
    at org.apache.http.impl.io.AbstractSessionInputBuffer.fillBuffer(AbstractSessionInputBuffer.java:149)
    at org.apache.http.impl.io.SocketInputBuffer.fillBuffer(SocketInputBuffer.java:110)
    at org.apache.http.impl.io.AbstractSessionInputBuffer.readLine(AbstractSessionInputBuffer.java:264)
    at org.apache.http.impl.conn.DefaultResponseParser.parseHead(DefaultResponseParser.java:98)
    at org.apache.http.impl.io.AbstractMessageParser.parse(AbstractMessageParser.java:252)
    at org.apache.http.impl.AbstractHttpClientConnection.receiveResponseHeader(AbstractHttpClientConnection.java:281)
    at org.apache.http.impl.conn.DefaultClientConnection.receiveResponseHeader(DefaultClientConnection.java:247)
    at org.apache.http.impl.conn.AbstractClientConnAdapter.receiveResponseHeader(AbstractClientConnAdapter.java:219)
    at org.apache.http.protocol.HttpRequestExecutor.doReceiveResponse(HttpRequestExecutor.java:298)
    at org.apache.http.protocol.HttpRequestExecutor.execute(HttpRequestExecutor.java:125)
    at org.apache.http.impl.client.DefaultRequestDirector.tryExecute(DefaultRequestDirector.java:645)
    at org.apache.http.impl.client.DefaultRequestDirector.execute(DefaultRequestDirector.java:464)
    at com.ibm.team.jfs.app.http.client.internal.ExtensibleRequestDirector.execute(ExtensibleRequestDirector.java:149)
    at com.ibm.team.lpa.common.clients.LpaRequestDirector.internalExecute(LpaRequestDirector.java:180)
    at com.ibm.team.lpa.common.clients.LpaRequestDirector.execute(LpaRequestDirector.java:159)
    at com.ibm.team.lpa.common.http.client.cache.HttpClientCache.executeCacheMiss(HttpClientCache.java:205)
    at com.ibm.team.lpa.common.http.client.cache.HttpClientCache.execute(HttpClientCache.java:116)
    at com.ibm.team.lpa.common.http.client.cache.HttpClientCache.execute(HttpClientCache.java:87)
    at com.ibm.team.lpa.common.http.client.cache.HttpClientCacheDirector.execute(HttpClientCacheDirector.java:30)
    at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:820)
    at com.ibm.team.lpa.common.clients.CommonHttpClient.execute(CommonHttpClient.java:100)
    at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:919)
    at com.ibm.team.lpa.common.http.client.cache.ChangeEventClient.getFeed(ChangeEventClient.java:96)
    at com.ibm.team.lpa.common.http.client.cache.ChangeEventMonitor$MasterRunnable.processChangeEvents(ChangeEventMonitor.java:282)
    at com.ibm.team.lpa.common.http.client.cache.ChangeEventMonitor$AbstractRunnable.run(ChangeEventMonitor.java:185)
    at com.ibm.team.lpa.common.http.client.cache.ChangeEventMonitor$1.run(ChangeEventMonitor.java:450)
    at java.util.Timer$TimerImpl.run(Timer.java:296)

and prevents log in: what could be the reason ?